Comparative analysis of the human type 1a and bovine type 1 papillomavirus genomes.

The DNA sequences of the genomes of the bovine type 1 and human type 1a papillomaviruses were compared. The overall organization of both genomes is very similar. Three areas of maximal homology were found in the L1 and E1/E2 genes, and at the beginning of L2. The conservation of homologous amino acid sequences encoded in the open reading frames argues that these segments represent real genes or exons. Within these segments, however, only certain domains of the putative proteins are preferentially conserved. Two polypeptide chains show homologous arrangement of the cysteine residue clusters Cys-X-X-Cys, despite a lack of conservation of the rest of the amino acid sequence. A significant sequence divergence in a region where the three reading frames are open suggests that papillomavirus genomes have evolved not solely by accumulation of point mutations. Conserved sequences were also found in the noncoding region, and their possible involvement in regulation of viral gene expression is discussed.     

Absence of nucleosomes in a histone-containing nucleoprotein complex obtained by dissociation of purified SV40 virions

Reduction of disulfide bonds involving the major capsid protein with dithiothreitol and removal of the calcium ions by EGTA disrupts the simian virus 40 virions. This process yields normal circular viral minichromosomes containing the four core histones and traces of the capsid proteins at pH values higher than 8.5. However, when carried out at pH 7.5, this procedure yields nucleoprotein complexes that contain both histones and the viral structural proteins. These pH 7.5 complexes appear as circular structures with a mean of 93 +/- 17 beads with a diameter of 7 nm and no visible nucleosomes when observed by electron microscopy. In contrast to the compaction of the viral DNA in minichromosomes, the length of these beaded structures is roughly the same as free DNA. We suggest that VP1, the major capsid protein, can act as a nucleosome unfolding agent in neutral pH and low ionic strength.     

Location of the T4 gene 32 protein-binding site on polyoma virus DNA

Three easily denatured regions can be demonstrated in polyoma virus DNA. T4 gene 32 protein which binds to single stranded DNA, but not to duplex DNA, will specifically bind to any of these sites when viral DNA is in its superhelical configuration. These sites were mapped relative to a unique E. coli R_I endonuclease cleavage site by electron microscopy.     

A single mutational modification of a tryptophan-specific transfer RNA permits aminoacylation by glutamine and translation of the codon UAG

In this work we show that the wild-type (su^?7) progenitor of the recessivelethal suppressors of UAG (su⁺7(UAG)) and of UAA/G (su⁺7(UAA/G)) is the structural gene for transfer RNA^Trp, the adaptor for translating the codon UGG. The su⁺7(UAG) suppressor form of the tRNA has a C for U substitution in the middle base of the anticodon; in the su⁺7(UAA/G) suppressor tRNA both C residues of the anticodon are replaced by U. Our data establish that the mutational change altering the tRNA^Trp to a UAG suppressor is accompanied by a loss of tryptophan-accepting specificity and the acquisition of glutamine-acceptor activity.