The virus‐like particles (VLPs) of the yeast retrotransposon Ty are genetically, structurally and functionally analogous to retroviral nucleocapsids or cores. Like retroviral cores Ty‐VLPs package and possibly promote the enzyme activities for reverse transcription and integration, as well as encapsulating the RNA that is the intermediate in retrotransposition. Here we show that Ty‐VLPs assemble into symmetrical structures across a broad distribution of particle sizes. This spread of sizes violates the principle of quasi‐equivalent packing. In addition, RNase accessibility experiments suggest that these particles form an open structure that does not protect the encapsulated RNA. These features distinguish Ty‐VLPs from typical spherical viral capsids in both structure and function.

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A rare cDNA coding for most of the alpha subunit of the Torpedo nicotinic acetylcholine receptor has been cloned into bacteria. The use of a mismatched oligonucleotide primer of reverse transcriptase facilitated the design of an efficient, specific probe for recombinant bacteria. DNA sequence analysis has enabled the elucidation of a large part of the polypeptide primary sequence which is discussed in relation to its acetylcholine binding activity and the location of receptor within the plasma membrane. When used as a radioactive probe, the cloned cDNA binds specifically to a single Torpedo mRNA species of about 2350 nucleotides in length but fails to show significant cross-hybridisation with alpha subunit mRNA extracted from cat muscle.

Monomer chromatin particles containing 140 base pairs of DNA and eight histone molecules have been studied by neutron scattering. From measurements in various H20/D20 mixtures, radii of gyration and the.-average scattering density.of the particle were determined. The radius of gyration under conditions when scattering from the DNA dominates is 50A, and when scattering from the protein dominates, 30A. Consequently the core of the particle is largely occupied by the histones while the outer shell consists of DNA together with some of the histone.

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