Lambda phage

About: Lambda phage is a research topic. Over the lifetime, 1609 publications have been published within this topic receiving 84675 citations. The topic is also known as: Enterobacteria phage lambda.

Bacteriophage Evolution and the Role of Phages in Host Evolution

Abstract: Comparative analyses of phage genome sequences imply that a major component of phage evolution is large numbers of intrinsically very improbable events In addition, there are comparable numbers of prophage sequences that are found in the genomic sequences of bacteria and, sometimes, archaea There are stretches of sequence that match well, with abrupt transitions to regions with no detectable similarity or sometimes a different level of similarity These transition points are considered the products of nonhomologous recombination events in the ancestry of one of the phages being compared; in this sense, they are fossils of past events in the history of the genome It is believed that there are at least two factors that can restrict the horizontal flow of genes across the expanses of phage sequence space Many of the beneficial genes carried by prophages appear to be morons, ie, the genes that have entered the genome recently and are typically flanked by a transcription promoter and a terminator The understanding of how phages evolve began in the late 1960s with the hetero duplex mapping of the chromosomes of phage lambda and some close relatives, showing that these molecules are mosaic with respect to each other Genome sequences for such phages are just now becoming available, and the largest genome to date is 10 times as big as that of phage lambda, with a corresponding increase in gene number

Analysis of transcription termination signals in the nin region of bacteriophage lambda: the roc deletion.

Abstract: Deletions in the region, nin, between the P and Q genes of phage lambda remove a portion of the phage genome that includes signals for termination of transcription. These deletions were selected because they permit growth of lambda derivatives defective in the N-mediated transcription antitermination system; i.e., the deletions confer N independence (nin). Thus nin phages (e.g., lambda nin5) grow in most Escherichia coli nus mutants. The nus genes encode functions necessary for N action. We report the isolation of a deletion in the nin region delta roc that confers a partially N-independent phenotype; lambda derivatives with delta roc can grow under normally nonpermissive conditions, 32 degrees C, in a host with the rpoB-nusC60 mutation. The roc deletion also partially suppresses the inhibitory effects of other nus mutations at higher temperatures. Delta roc, which extends from base pairs 41883 to 43825, overlaps the nin5 deletion, which extend from base pairs 40501 to 43306. Unlike the nin5 deletion, the sequences deleted by delta roc do not include a stem-loop structure, tR2, previously shown to have terminator activity. Using promoter and terminator testor vectors, we demonstrate that a 2,400-base-pair fragment that includes the wild-type roc region but excludes tR2 has terminator activity. Thus, delta roc permits a functional division of the transcription termination signals in the nin region.

Transcription of a region downstream from λ ori is required for replication of plasmids derived from coliphage lambda

Abstract: DNA replication of lambda phage depends on transcriptional activation at or around the λori region by RNA polymerase. To elucidate the function of the transcriptional activation, we constructed several plasmids carrying λori and lacP, whose relative locations and directions were different from each other, and studied replication activity of these recombinant plasmids. Transcription in a region immediately downstream from λori, but not in the λori region, was found to be essential for plasmid replication. Transcription proceeding over a certain minimal length was required and only rightward-directed transcription was effective for the activation