Yeast amber suppressors corresponding to tRNA3Leu genes

Amber suppressors previously isolated from the yeast Saccharomyces cerevisiae and belonging to the same phenotypic class (Liebman et al., 1976) were assigned to nine different linkage groups named SUP52 through SUP60. One of these suppressors, SUP52, had been shown to cause the insertion of leucine and had been genetically mapped (Liebman et al., 1977). The following additional amber suppressors were mapped: SUP53 maps near the centromere of chromosome III closely linked to leu2; SUP54 maps on chromosome VII, 6 cM distal to trp5; SUP56 maps on chromosome I, 5.4 cM distal to ade1; SUP57 maps on chromosome VI, closely linked to met10; and SUP58 maps on the left arm of chromosome XI, loosely linked to met14. We show by protein analysis that like SUP52, the suppressors SUP53 through SUP56 are leucine-inserters. Furthermore, by hybridization with a cloned tRNA3Leu probe we demonstrate that at least SUP53, SUP54, SUP55 and SUP56 contain mutations in redundant tRNA3Leu genes because they each generate a new XbaI site in a DNA fragment encompassing a tRNA3Leu gene. These new XbaI sites are predicted by the known sequences of tRNA3Leu genes if the CAA anticodon mutates to the amber suppressing anticodon CTA. It is likely that each of the nine suppressors in this phenotypic class contain similar mutations in different tRNA3Leu genes since we find that there are approximately nine unlinked redundant copies of tRNA3Leu genes in haploid strains.     

DNase I cleavage of adenoviral nucleoprotein.

Cleavage products resulting from DNase I treatment of adenoviral nucleoprotein were examined by gel electrophoresis, Southern blotting and hybridization to cloned restriction fragments derived from various regions of the viral genome. DNase I produced specific double-stranded cleavages in DNA of purified adenoviral cores and in DNA of intranuclear viral chromatin at early and late times of infection. At least some of these sites were also cleaved by DNase I in purified viral DNA, showing that sequence specificity of DNase I cleavage may contribute to the observation of specific double-stranded DNase I cleavage sites in adenoviral nucleoprotein. In addition, sites were observed which were specific either for cores or for intranuclear chromatin. In contrast to many cellular genes which have been characterized, there was no obvious relationship between DNase I cleavage sites and other features of the viral genome such as promoters or polyadenylation sites.