Showing papers in "Annual Review of Microbiology in 1991"

Prokaryotic osmoregulation: genetics and physiology.

Abstract: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 570 MECHANISMS UNDERLYING OSMOREGULATORY RESPONSES.... . . .. .. . . . . . .. .. 571 Homeostasis vs Adaptation to Change. . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . 571 Examination of Possible Signals . . . . . ...... . . . . . . . . . : 573 PHYSIOLOGY OF OSMOTIC REGULATION . . . . .. .. . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 581 Compatible Solutes Synthesized and/or Transported . . . . . . . . . . . . . . . . . 581 Osmoregulation of the Periplasm . . . . . . . . ... . . . . . . . .... . . . . . . . ..... . . . . . . . .. . . . . 588 GENES AND PROTEINS . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . 588 The EnvZ/OmpR-Dependent Expression of the ompF and ompC Genes of E. coli K-12 .. . . . . . . . ..... .. . .. ....... . . . . . ....... . . . . . . ..... . . . 589 The kdpABC operon of E. coli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 The proU Operon of E. coli and S. typhimurium . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 593 Other Osmoregulated Genes. . ......... 597

Putative virulence factors of Candida albicans.

Abstract: INTRODUCTION 187 Hypothetical Set of Virulence Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 188 Commensal or Opportunistic Pathogen? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Purpose of Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 HYPHAL PRODUCTION 190 Early Observation . . . . . . . . . .. . . , .... .. .. . . . . .. . . .. .. ...... . . . . . . . . .. . . . . . . .. .. . . . . . ,. 190 Inherent Experimental Diff iculties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 191 Recent Observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 193 Other Approaches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 PROTEINASE ACTIVITy 197 Is There Only One Proteinase? 198 Evidence For and Against Proteinase . .... . . . . . . . . . . . . . . ....... ... . . . . . . ....... . . . . . .... . . ... 1 99 ADHERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 203 Classification of Receptor-Ligand Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 How Many Receptor-Ligand Molecules on C. albicans Are There? . . . . . . . . . . . . . . .... . 205 Virulence Role . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 VARIABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Chromosomal Instabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Antigenic Variabilit y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 208 OTHER ATTRIBUTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,.. . . ...... . . . . . 209 Suppression-Activation of Host-Acquired Specific Immunity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 CONCLUDING REMARKS 209

Serine beta-lactamases and penicillin-binding proteins.

Abstract: The Penicillin-Interactive, Active-Site Serine Protein Family . . . . . .... . . . . .. . . . . . . . . . . . . . 37 The Low-Mr PBPs . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . ... . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . 45 The (3-Lactamases and the Penicillin Sensory-Transducer BLAR ...... . . 47 The Atomic-Level Enzyme-Ligand Interactions . . . . . .. . . . . . . . . . .. . . . . . . . .. . . . . . . . . . .. . . . . . . . . 50 The High-Mr PBPs of Class A and B .... . . . . . . . ...... . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 54 Intrinsic Resistance by Emergence of Altered High-Mr PBPs . .. . . . . . . . . . . . . . . . . .. . .. . . . 58

Plant Genetic Control of Nodulation

Abstract: INTRODUCTION 345 LEGUME NODULATION . . ........ ....... ... .. ... . . ....... ..... ........ . 346 ROLE OF THE BACTERIAL SYMBIONT: SIGNAL EXCHANGE 348 NODULATION AS A DEVELOPMENTALLY REGULATED PHENOMENON....... 354 PLANT NODULATION MUTANTS 357 NODULATION CONTROL IN LEGUMES 361 AUTOREGULATION ...... ........ 362 What Is the Signal Transduction Mechanism? an Example of Systemic Root-Shoot Interaction .... .. . .. .... .. ....... ""'''''''''''''''''''''''''' .. " .. ,," 363 How Is Nodulation Suppressed? " 364 What Triggers the Systemic Response?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 A Working Hypothesis. . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . ... .. . 367 NODULATION IN THE ABSENCE OF RHIZOBIUM SPP. 368 PERSPECTIVES 370

The Universally Conserved GroE (Hsp60) Chaperonins

Abstract: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . .. . . .. . . . . ... ...... . . . . . . . . . . . . . . . . ... . . . . . . . . . . 301 THE groE OPERON . . . . . . . . . . . .... . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 THE GroE PROTEINS . . . . . . . . . . . . .. ... . . . . . . . . . . .. , 303 EVOLUTIONARY CONSERVATION OF groES AND groEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 FUNCTION OF THE groE GENES IN BACTERIOPHAGE MORPHOGENESIS. . . . . . 308 The Bacteriophage T4 Case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 An In Vitro System for A Preconnector Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 FUNCTION OF THE GroE PROTEINS IN E. COLl PHy SIOLOGy . . . . . . . . .. . . . . . . . . . . . 311 Phenotypes Associated with groE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 Function of the groE Gene Products in Protein Folding, Oligimerization, and Export . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 DEFINING SUBSTRATES OF GroE CHAPERONINS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Folding and/or Export of Pre-f3-Lactamase . . . . . . . . . . ......... 315 A MODEL FOR GroES-GroEL ACTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

POLYMERASE CHAIN REACTION: Applications in Environmental Microbiology

Abstract: INTRODUCTION ........ .. .. . . . ........ . 138 THE POLYMERASE CHAIN REACTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 1 38 PCR Reaction Mixture . . . . . . . .. . ........ 138 PCR Reaction Conditions ........ . . . . . . . . ....... . . . . 140 Multiplex PCR . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . .. . . . . . . . .. ... ... .. ....... . . . . . 1 4 1 Enhancing PCR Efficiency .. . ... . . . . . . . . . . . . 141 ISOLATION OF ENVIRONMENTAL NUCLEIC ACIDS FOR PCR . . . . . .. . . . . ....... . . . 142 Isolation of Nucleic Acids from Aquatic Environments.. . .. . . .... ........ . . ..... 142 Isolation of Nucleic Acids from Soil and Sediment . . .. . . . ....... . . 143 DETECTION OF PCR PRODUCTS .... . . . . . . ..... . . . . . . .... . . . . .. . . . . . . . . . . . . . . . . . . . . . ..... . . . . . 144 Capture Probes-Reverse Hybridization . .... . . . . . .. . .... . . . . . . . . 146 USE OF PCR TO DETECT MICROORGANISMS IN ENVIRONMENTAL SAMPLES 147 Detection of Genetically t;ngineered Microorganisms .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Detection of Indicator Organisms and Pathogens... . . . . . . . . . ...... . . . . . . . . . . . . ....... . . . . . 148 QUANTITATION OF PCR-AMPLIFIED PRODUCT . . . . . . . . . . . . . . . . . .. ...... . . . . .... . . . ..... 149 Quantification of DNA Target Sequence . . . . .. . ... . .. . . . . . . .. . . . ....... .. . . .. . . .. . ...... . . . . . 149 Quantification of mRNA .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 50 USE OF PCR TO ISOLATE AND CLONE SPECIFIC DNA SEQUENCES ... . . ....... 1 52 Use of PCR to Analyze Ribosomal RNA Sequences ....... . . . . . . . . . ........ . . . 152 Cloning DNA and Creating Gene Probes Using Degenerate Primers ... ........ . . . ... 153 CONCLUSION . . . . . . . . . . .. . . . . . .... . ......... 1 55

Chaperone-Assisted Assembly and Molecular Architecture of Adhesive Pili

Abstract: The assembly of bacterial pili as exemplified here by P and type 1 pili of E. coli is a complex process involving specific molecular interactions between structural and chaperone proteins. The assembly process occurs postsecretionally, i.e. after the subunits are translocated across the cytoplasmic membrane. In a single cell, hundreds of thousands of interactive subunits are typically surface localized and assembled into pili. Periplasmic chaperones are generally required to bind to the interactive subunits and partition them into assembly-competent complexes. The binding of the chaperone to the subunits apparently protects the interactive surfaces and prevents them from aggregating at the wrong time and place within the cell. Pili are most likely assembled into linear polymers that package into right-handed helices after their translocation through specific outer-membrane channels. Each pilus filament is a quaternary assembly of the structural subunit and several minor subunits including the adhesin moiety. Although the assembly and organization of P and type 1 pili are very similar, there are some notable differences. For example, the P pilus adhesin is located exclusively at the tips of the pilus filament and forms part of a morphologically distinct structure. In contrast, the adhesion moiety of type 1 pili is inserted into the pilus filament at intervals, but only the adhesin molecule exposed at the pilus tip is functional. The variability in isoreceptor recognition amongst P pili has been solely ascribed to structural differences in the respective adhesin molecules, whereas in type 1 pili, variability in binding specificity has been attributed to the pilus filament that influences the conformation of the adhesin moiety. Less is known about the structure or assembly of type 4 pili, which are a unique class of pili expressed by several different species of gram-negative bacteria. The phase variation of the pilC assembly gene in N. gonorrheae to the off state results in the accumulation of unassembled subunits toxic to the cells. This process exerts a strong selection pressure on the cells that triggers alterations in the pilin structural gene. Thus, antigenic variation of pili in this organism may be regulated at the level of assembly. Finally, the concept of periplasmic chaperones in postsecretional assembly is most likely a general phenomenon in the biology of gram-negative bacteria. The investigations of pilus assembly will continue to provide insight into the details of how macromolecular assembly reactions are coordinated in the bacterial cell and how the regulation of assembly genes can profoundly affect biological processes.

Gene amplification in Leishmania

Abstract: INTRODUCTION . . . . . . . . . . . . .. . .... . . .... . . . . . . . . . . . . . . . . . . . . . .. . ... . . . .. . . . .. . . .. . . .. .. . .. . . . . . . . . . . 417 A Leishmania Primer 4 1 8 The Leishmania Genome and Circular DNAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 9 MULTIPLE MECHANISMS O F DRUG RESISTANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 GEN ES AMPLIFIED IN RESPONS E TO DRUG PRESSURE . . . . . . . . . . . . . . . . . . . . ... . . .. . . 421 Dihydrofolate Reductase-Thymidylate Synthase. . . .. .. . . ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 The H Region: a Complex Multiple Drug-Resistance Element 422 Tunicamycin and Glycosyltransferase 425 ODC, IMPDH, and Classic MDR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 425 M ISCELLANEOUS AMPLIFIED GENES . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 T and D DNAs . . .. . . . .. . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. .. . .. . .... .. . . . ... .. . . . . .. . . . . 426 Miniexon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 Subchromosomal Amplifications . . . . . . . . . . . . . . . . . 427 What Leads to the Emergence of Apparently Nonfunctional Amplified DNAs? . .. . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428 FREQUENCY OF GENE AMPLIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 STRUCTURE OF EXTRACHROMOSOMAL AMPLIFIED DNAs .... . . . . . . . . . . ... ... .... 429 Simple, Time-Invariant Direct and Inverted Amplifications . .. . . . . . . . . . . . . . .. . .. .. . . . . . . . 430 Unstable and Stable Amplification 430 Recurrence of Rearrangements Involving Repetitive DNA Sequences . . . . . . ... . . . . . . . . . 431 Functional Genetic Elements Within Amplified DNAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 1 Comparisons with Amplified DNAs in Cultured Mammalian Cells 432 Three Chromosomal Types of Amplification . .. . . . . . . .. . ... . . . . . . . .. . . . . . ... .. . . . ........ .. . . 432 M ECHANISM OF GENE AMPLIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 ROLE OF GENE AMPLIFICATION IN LEISHMANIA BIOLOGY AND EVOLUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 Clinical Drug Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 Amplified Genes in Leishmania: a Bridge Between Prokaryotic Resistance Factors and Mammalian Gene Amplifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 Role of Amplification in Shaping the Parasite Genome . . . . . . . . . . . . . . . . ...... . . . .. . . . . . . . . 438 PROSPECTUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . 439

Control of carbon and nitrogen metabolism in Bacillus subtilis.

Abstract: CARBON CATABOLITE REPRESSION 108 Sugar Transport 109 Mutants Affected in Carbon Catabolite Repression ..... . . . . . . . . . ..... . . 112 Carbohydrate Metabolism Genes '" 113 Other Genes Subject to Carbon Catabolite Repression 119 NITROGEN CATABOLITE REPRESSION . ... . . ..... . . . . . . . . . .. . . . . ...... . . ...... . . . . . .. . . . ... 119 Ammonia Assimilation Systems 120 Other Genes Induced by Nitrogen-Source Limitation 123 Regulation by Amino Acids .. . . . ....... . ........ . ..... . . . . . . . . . . . . . .. . . . . . . 123 CATABOLITE REPRESSION OF SPORULATION...... . ....... ........ . . ..... . . ........ . ... 124

Genetically engineered baculoviruses as agents for pest control.

Abstract: INTRODUCTION . . . . . . . . ... . . . . .... . . . .... . . . . ... . . . . ..... . . .... ....... . . . .... . . . ... . . . . . 69 BACULOVIRUS BIOLOGY AND LIFE CyCLE . . . . . . . . . . . . . . . . . . . . . . . . . ... ...... . . . . . . .. .. . 70 Classification and General Properties 70 Infection and Replication in Insects 71 BACULOVIRUSES AS VIRAL INSECTICIDES .. . . . . . . : 74 FACTORS CONSTRAINING GREATER USE OF BACULOVIRUS PESTICIDES . . . 7S GENETICALLY ENHANCED VIRAL PESTICIDES . .... ..... ......... . . . . . .. .. . . . .. . . . . .. . . 76 ENGINEERING STRATEGIES .. .. . . . ... . . . . . .. . . . . . . ... . . . . .. . . . . . . .. ....... . . . . . . . . . . . . ... . . . . . . 78 ENVIRONMENTAL ISSUES .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... .. ... . . . . .... . . 80 FIELD-RELEASE TESTING . . . . .. . . .... . .. .. . . .. . . . . . ..... . . . .. . . . . . . . .. . . . . . . .. . . . . ... .. . ... . . ... 81 FUTURE: PROMISES AND PITFALLS.... . ..... . . . . . ....... . 84

Ivermectin as an antiparasitic agent for use in humans.

Abstract: INTRODUCTION.. . . . . . . ........ . . .. . . . .. . . ..... . ...... . . . . .. . . . . .... . . .. . .... 446 INTESTINAL NEMATODES . . ........ . . . . .. . . . . .. . . . . . .. . . . . . . . . . . . . . .. . ......... . .. .. . . ....... . . 446 A scaris lumbricoides ..... . . . . .... ... . . . .. . . . . .. ..... 446 Ho.okwo.rm� (�ncylostoma, Necator). ..... . . .... . . .. . . . . . . . . . . . . . . ..... . . . . . . . . 446 Tnchuns tnchlUra . .. . . . . . . . ..... ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 Enterobius vermicularis. ..... . . . ..... . . ......... . . .. . . . . . . . . . . . . . .. . . .... . ... . . ....... 448 Strongyloides stercoralis....... . . . . . . . . . . .. . . . . . . .. . . .... . . . . . . . . . . . ........ . . . . . 448 Broad-Spectrum Potential 449 ONCHOCERCIASIS. . . . . . . . . . . . . . . . . . . . . . . . ...... . . . . . . . .. 449 Early Hospital-Based Probes (Phase J) ..... . ..... .. ... . . . .... . . .. . . . . . .... . ... . .. .. 450 Hospital-Based Trials with Reference Treatment (Phase 1/) ... . . . . . . . . .. . 451 Large-Scale Hospital-Based Trials (Phase III) 453 Large-Scale Community-Based Trials (Phase IV) . . . . .. . . . . . . . . . .... ...... .... . . . . ....... . . 454 Effect on the Parasite 455 Effect on Transmission 459 Causal Prophylaxis 461 OTHER FILARIAL INFECTIONS . . . . . . .. . .... . . . .. . . .... . . . .... . . . . . . . . .. . . . . .... . . ... 461 Wuchereria bancrofti ... . .. . .... ....... . ........ . . . . . . .. . . . . . . . . . . ... . . 461 Brugia, Mansonella, Loa.... . . . . . . . . . . .. .. . . .... . . . 464 EFFICACY AGAINST OTHER PARASITES . ... . ... . ... . . . . .. . . . . . . . . . . ......... . . . . . . ....... 464 SAFETY IN HUMANS . . . . . . . . . . . . . . . . ..... .. ... . . . . . . . . . . . .. 465 Safety and Tolerability in Onchocerciasis 465 Safety in Other Infections. . .. .. .... . . . . .... . . . . . . . . ..... . . . . . .... 467 Safety in General 467 CURRENT DRUG DISTRIBUTION..... . . . .. . . . . . . . . . . . .. . . . . . . ..... .... . . . ...... . . . 468

Proper and improper folding of proteins in the cellular environment.

Abstract: Protein folding in the cellular environment involves an interplay between the intrinsic biophysical properties of a protein, in both its folded and unfolded states, and various accessory proteins that aid the process. Factors such as peptidyl prolyl isomerase, protein disulfide isomerase, thioredoxin, and SecB may interact with the unfolded forms of specific classes of proteins, while members of the hsp70/DnaK and hsp60/GroEL molecular chaperone families may play a more general role in folding. Secretion, proteolysis, and aggregation are other in vivo processes that depend greatly on the folding behavior of a given protein. Intrinsic folding rates, or even translation rates, of nascent proteins may be optimized by natural selection to ensure smooth coordination with all the cellular components required for a successful folding reaction.

Mechanisms of natural resistance to human pathogenic fungi.

Abstract: Natural host-resistance mechanisms are essential first-line defenses against most mycotic agents; however, these defenses are often not sufficient for complete protection. The host relies on the immune responses to provide the additional antifungal activity necessary for maximum protection. In systemic mycotic diseases, the immune system must be functional to prevent the host from succumbing to the disease. Natural resistance mechanisms act together in a coordinated manner early in the disease process to either kill or prevent the fungal agent from proliferating and gaining entrance to other tissues. The early defensive measures of the natural effector mechanisms are usually sufficiently effective to provide time for the generally more effective immune defenses to develop. Together, the natural defenses and the immune defenses regulate each other through cytokine networks, and generally these systems provide the host with adequate protection against threatening mycotic agents.

RNA editing in trypanosomatid mitochondria.

Abstract: INTRODUCTION 327 kDNA 328 Ma.ti circle s .... 329 Mi nicircle s . . ..... . . . . . . . ......... . . .. . . . . . . . . . . . .. . .. . . ... . . . . . . . .. . . . . . . . ...... . . . . . . 329 kDNA Mutati o ns . . .. ... . .... . . .. . .. . .. . . .. . . . . .. . .. ... . . . . ... ..... . .. .. . . . . . . . . . . . . .. .. . . . . . . . . 331 RNA EDITING IS TRANSCRIPT AND TRANSCRIPT-REGION SPECIFIC 332 E diti ng of Re stricte d Reg i o ns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... 332 Exte nsive E diti ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 CONSEQUENCES OF EDITING 334 GUIDE RNA 335 g RNA Characteri stics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 g RNA C o di ng Seque nce s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 PA RTIALL Y EDITED mRNAs 337 Junctio ns. . . . . . . ..... .. . . . ... . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . ... . . . . . ... 337 Mo dels of g RNA Usag e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 The E diting Machine ry ........ 340 DEVELOPMENTAL REGULATION 340 PERSPECTIVE. . . . . ..... .... ... . . . . . . . .... ...... ..... 341

Techniques for Selection of Industrially Important Microorganisms

Abstract: The screening of microorganisms for the production of useful products continues to be an important aspect of biotechnology. Although advances in instrumentation, genetics, and microbial physiology are having an impact, screening programs are still primarily based on so-called classical techniques of enrichment and mutagenesis. One area that needs strengthening is the advancement of knowledge in microbial physiology. Recent surveys indicate that industry leaders see trained microbial physiologists as being the limiting factor in development of biotechnology in the coming decade. The largest impediment to development of new screening techniques is the ironic lack of programs specifically directed at developing new techniques. Too much emphasis is placed on using available techniques and relying on sheer labor and screening of vast numbers of organisms to produce novel products. In this respect, the Japanese are the exception and have proven that the establishment of new programs is worth the cost and effort. They are undoubtedly the world leaders in development of screening techniques and consequently the discovery of novel products. The isolation of microbes from novel and extreme environments holds tremendous promise in two areas. First, as Omura (46) and others (9, 48, 65) state, novel organisms will yield novel products. Second, such organisms serve as models for the understanding of structure and function that will facilitate the genetic manipulation of organisms and advance our ability to engineer novel enzymes. Hopefully such advances will enable genetic and protein engineering to have a greater impact on screening programs and techniques in the future. The earth holds a vast amount of varied and unique environments, from natural extremes such as high-altitude deserts and thermal springs, to manmade environments such as industrial-waste-treatment facilities, from which, with the appropriate methods and techniques, we may isolate and evaluate new potential products.

msDNA and bacterial reverse transcriptase.

Abstract: msDNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Genetic Locus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BIOSYNTHESIS OF msDNA . Requirement for Reverse Transcriptase . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biosynthetic Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REVERSE TRANSCRIPT ASE . Genetic Locus . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Nuclear fusion in yeast.

Abstract: PERSPECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539 PATHWAY OF NUCLEAR FUS ION . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 Mating and Nuclear Fusion . . .. .. . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . ... . .. .... . . . . . . ... 540 Mutations That Block Nuclear Fusion . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ... . . . .. . 544 Assays for Nuclear Fusion.... . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... 545 Unilaterality Versus Bilaterality . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 GENES REQUIRED FOR NUCLEAR FUS ION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 KARl . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 549 KAR3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 BIKI .. . . . . . . . . .... . . . . . . . . . . . . . . . .. .. . . ... .. . .. ..... . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . ...... 555 KAR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 556 CDC4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 KEM Genes. . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . .... . . . . 558 CINI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559 CIK Genes . . . . . . ........ ..... . . . . . . . . . . . . . . . . ..... . . . . . . 560 CDC28 , CDC34, and CDC37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560 MODELS FOR NUCLEAR FUS iON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561 CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563