Env gene products of AKR dual-tropic viruses: examination of peptide maps and cell surface expression.

The env gene products of nine AKR dual-tropic murine leukemia viruses were compared by peptide mapping and were assayed for expression on the cell surface of infected fibroblasts. Seven virus isolates expressed the env gene polyprotein on the cell surface. The env gene products of six of the seven viruses had identical peptide maps. The analysis of structure and expression of env gene products carried out in this study characterizes a subset of dual-tropic murine leukemia viruses shown by others to be thymotropic.

Altered mitochondrial ribosomes in a cold-sensitive mutant of Saccharomyces cerevisiae.

A mutation at a new locus denoted tsr1 which lies very close to the ery1 locus and 21S rRNA gene in mitochondrial DNA of Saccharomyces cerevisiae, confers conditional respiratory deficiency on cells grown at low temperature, namely 18 degrees. Studies on mitochondria isolated from a strain carrying the mutatated tsr1 locus demonstrate that the rate of mitochondrial protein synthesis is cold-senitive at 18 degrees. The large subunit of the mitochondrial ribosomes isolated from the mutant strain is unstable during extraction and the isolated ribosomes are shown to be defective in catalyzing the poly U-directed synthesis of polyphenylalanine. It is concluded that the tsr1 locus is involved in the determination of the properties of the large subunit of the mitochondrial ribosome.