Because of the high degree of organizational complexity of eucaryotic cells, it is clear that the implementation of their genetic programs must, in many cases, involve a complex sequence of cotranslational and posttranslational events that are necessary to transfer polypeptides from their sites of synthesis to their sites of function. It is difficult to envisage the existence of a single general mechanism that would ensure that all polypeptides released from ribosomes attain their correct subcellular destination . This is because there are, in a eucaryotic cell, at least as many possible destinations for a newly synthesized polypeptide as there are different compartments and membrane systems. Moreover, it is not likely that completed and fully folded polypeptides, with their charged and polar residues exposed to the aqueous environment, could freely traverse hydrophobic barriers constituted by phospholipid bilayers, which are the universal feature of all cell membranes (208). Instead, it may be expected that special mechanisms have evolved that direct polypeptides to specific membranes and, when necessary, assist them in their passage across the hydrophobic barriers . These mechanisms must involve specific receptors for structural features ofthe polypeptides and may entail conformational changes or even extensive structural modifications of the polypeptide, as well as the expenditure of energy . In this paper we consider mechanisms for the transfer of newly synthesized polypeptides to their sites of function in different subcellular membranes and organelles, and discuss models in which specific features ofthe polypeptides serve as signals to direct them along selected subcellular pathways to their final destination . These signals may act during translation or after synthesis of the polypeptide is completed and may or may not be removed from the initial product of translation . Transient or permanent signals within polypeptides destined to membranes would also account for the final characteristic orientation of membrane proteins with respect to the phospholipid bilayer . Several other reviews discussing various aspects of this subject have recently appeared (15, 44, 53, 117a, 127, 243a) .

https://rupress.org/jcb/article-pdf/92/1/1/1075487/1.pdf

Mechanisms for the incorporation of proteins in membranes and organelles.

The generation of distinct neuronal cell types in appropriate numbers and at precise positions underlies the assembly of neural circuits that encode animal behavior. Despite the complexity of the vertebrate central nervous system, advances have been made in defining the principles that control the diversification and patterning of its component cells. A combination of molecular genetic, biochemical, and embryological assays has begun to reveal the identity and mechanism of action of molecules that induce and pattern neural tissue and the role of transcription factors in establishing generic and specific neuronal fates. Some of these advances are discussed here, focusing on the spinal cord as a model system for analyzing the molecular control of central nervous system development in vertebrates.

https://science.sciencemag.org/content/sci/274/5290/1115.full.pdf

Diversity and Pattern in the Developing Spinal Cord

Retroviruses have proved to be useful reagents for studying genetic and epigenetic (such as regulatory) changes in eukaryotic cells, for assessing functional and structural relationships between transposable genetic elements, for inducing insertional mutations, including some important in oncogenesis, and for transporting genes into eukaryotic cells, either after natural transduction of putative cellular oncogenes or after experimental construction of recombinant viruses. Many of these properties of retroviruses depend on their capacity to establish a DNA (proviral) form of their RNA genomes as a stable component of host chromosomes, in either somatic or germinal cells.

http://science.sciencemag.org/content/sci/216/4548/812.full.pdf

Form and function of retroviral proviruses

Complex splicing patterns of RNAs from the early regions of adenovirus-2

Identification of a protein linked to the ends of adenovirus DNA

Sequence from early region of polyoma virus DNA containing viral replication origin and encoding small, middle and (part of) large T antigens

Cleavage Maps of DNA from Adenovirus Types 2 and 5 by Restriction Endonucleases EcoRI and HpaI

The nucleotide sequences at the termini of adenovirus-2 DNA☆

A new restriction endonuclease from Streptomyces albus G

Cloned DNA from the EcoRI J fragment of EBV has been used as template for in vitro transcription experiments using cell-free extracts prepared from HeLa or KB cells. Two EBV specific RNAs each about 175 bases in length were synthesised and nuclease 51 mapping experiments determined that these in vitro products corresponded precisely to the in vivo species obtained from Raji cells. These two RNA molecules are transcribed by RNA polymerase III and in common with other pol III-synthesised RNAs the coding sequences contain intragenic control regions. The relative abundance of the two RNAs synthesised in vitro differs from that observed in vivo.

J. R. Arrand

Papers

Sequence from early region of polyoma virus DNA containing viral replication origin and encoding small, middle and (part of) large T antigens

Cleavage Maps of DNA from Adenovirus Types 2 and 5 by Restriction Endonucleases EcoRI and HpaI

The nucleotide sequences at the termini of adenovirus-2 DNA☆

A new restriction endonuclease from Streptomyces albus G

In vitro transcription of two Epstein-Barr virus specified small RNA molecules