No abstract

Mating type in the yeast Saccharomyces cerevisiae is determined by the MAT (a or a) locus. HML and HMR, which usually contain copies of a and a mating type information, respectively, serve as donors in mating type interconversion and are under negative transcriptional control. Four trans-acting SIR (silent information regulator) loci are required for repression of transcription. A defect in any SIR gene results in expression of both HML and HMR. The four SIR genes were isolated from a genomic library by complementation of sir mutations in vivo. DNA blot analysis suggests that the four SIR genes share no sequence homology. RNA blots indicate that SIR2, SIR3, and SIR4 each encode one transcript and that SIRI encodes two transcripts. Null mutations, made by replacement of the normal genomic allele with deletion-insertion mutations created in the cloned SIR genes, have a Sir-phenotype and are viable. Using the cloned genes, we showed that SIR3 at a high copy number is able to suppress mutations of SIR4. RNA blot analysis suggests that this suppression is not due to transcriptional regulation of SIR3 by SIR4; nor does any SIR4 gene transcriptionally regulate another SIR gene. Interestingly, a truncated SIR4 gene disrupts regulation of the silent mating type loci. We propose that interaction of at least the SIR3 and SIR4 gene products is involved in regulation of the silent mating type genes.The third chromosome of the budding yeast Saccharomyces cerevisiae ( Fig. 1) contains three loci, all capable of determining cell type by regulating the expression of other cell type-specific genes. Normally, however, only MAT (either MATa or MATa) is expressed, whereas HML and HMR remain unexpressed. The role of MAT in determining cell type in S. cerevisiae has been reviewed extensively (11,15,30,37,48). Briefly, haploids and diploids homozygous at MAT mate efficiently with cells of opposite mating type, but cells of the same mating type rarely mate. MATa/MATTa diploids do not mate but can sporulate when starved for nitrogen. Heterothallic (ho) strains possess a stable mating ability. Homothallic (HO) strains interconvert the MAT alleles at high frequency during mitotic growth and rapidly give rise to a population containing cells of both mating types, which can mate to form MATa/MATTa diploids (16,49). Mating type interconversion is the result of the transposition of a copy of sequences from HML or HMR (normally containing a and a sequences, respectively) to MAT (17,24,25,27,32,39,51). Thus, the two silent loci serve as donors and are said to contain cassettes of information.The two silent HM loci contain complete copies of mating type information (17, 39, 51) but are kept transcriptionally inactive by the products of four genes identified by mutational analysis and known as MAR (mating type regulator; 26), SIR (silent information regulator; J. Rine, Ph.D. thesis, University of Oregon, Eugene, 1979; 42), or CMT (change of mating type; 12). The four SIR genes are unlinked to the HM loci and encode gene products which act in tran...

Truncated recombinant dengue virus envelope protein subunits (80E) are efficiently expressed using the Drosophila Schneider-2 (S2) cell expression system. Binding of conformationally sensitive antibodies as well as x-ray crystal structural studies indicate that the recombinant 80E subunits are properly folded native-like proteins. Combining the 80E subunits from each of the four dengue serotypes with ISCOMATRIX® adjuvant, an adjuvant selected from a set of adjuvants tested for maximal and long lasting immune responses, results in high titer virus neutralizing antibody responses. Immunization of mice with a mixture of all four 80E subunits and ISCOMATRIX® adjuvant resulted in potent virus neutralizing antibody responses to each of the four serotypes. The responses to the components of the tetravalent mixture were equivalent to the responses to each of the subunits administered individually. In an effort to evaluate the potential protective efficacy of the Drosophila expressed 80E, the dengue serotype 2 (DEN2-80E) subunit was tested in both the mouse and monkey challenge models. In both models protection against viral challenge was achieved with low doses of antigen in the vaccine formulation. In non-human primates, low doses of the tetravalent formulation induced good virus neutralizing antibody titers to all four serotypes and protection against challenge with the two dengue virus serotypes tested. In contrast to previous reports, where subunit vaccine candidates have generally failed to induce potent, protective responses, native-like soluble 80E proteins expressed in the Drosophila S2 cells and administered with appropriate adjuvants are highly immunogenic and capable of eliciting protective responses in both mice and monkeys. These results support the development of a dengue virus tetravalent vaccine based on the four 80E subunits produced in the Drosophila S2 cell expression system.

Chinese hamster X mouse somatic cell hybrids segregating mouse chromosomes were examined for their mouse chromosome content using trypsin-Giemsa (GTG) banding and Hoechst 33258 staining techniques. Simultaneously, they were scored for the presence of 24 mouse enzymes. The results confirm the assignments of 11 genes previously mapped by sexual genetics: Dip-1 and Id-1 to chromosome 1; Pgm-2 and Pgd to 4; Pgm-1 to 5; Gpi-1 to 7; Gr-1 to 8; Mpi-1 and Mod-1 to 9; Np-1 and Es-10 to 14. They also confirm chromosomally the assignments of 3 genes that were made by other somatic cell genetic studies: Aprt to 8; Hprt and a-gal to the X chromosome. But most importantly, four enzyme loci are assigned to four chromosomes that until now were not known to carry a biochemical marker which is expressed in cultured cells: Trip-1 to 10; Dip-2 to 18; Acp-1 to 12; and Ak-1 to 2. Cytogenetic examination of clones showing discordant segregation of HPRT and A-GAL, suggested the assignment of a-gal to region XE→XF of the mouse X chromosome. The cytologic studies provide a comparison between data from sexual genetics and somatic cell hybrids and validate hybrid cell techniques. They provide evidence of the reliability of scoring chromosomes by GTG and Hoechst staining and stress the importance of identifying clones with multiple chromosome rearrangements. Striking examples of nonrandom segregation of mouse chromosomes were observed in these hybrids with preferential retention of 15 and segregation of 11 and the Y chromosome.

Mating type in the yeast Saccharomyces cerevisiae is determined by the MAT (a or alpha) locus. HML and HMR, which usually contain copies of alpha and a mating type information, respectively, serve as donors in mating type interconversion and are under negative transcriptional control. Four trans-acting SIR (silent information regulator) loci are required for repression of transcription. A defect in any SIR gene results in expression of both HML and HMR. The four SIR genes were isolated from a genomic library by complementation of sir mutations in vivo. DNA blot analysis suggests that the four SIR genes share no sequence homology. RNA blots indicate that SIR2, SIR3, and SIR4 each encode one transcript and that SIR1 encodes two transcripts. Null mutations, made by replacement of the normal genomic allele with deletion-insertion mutations created in the cloned SIR genes, have a Sir- phenotype and are viable. Using the cloned genes, we showed that SIR3 at a high copy number is able to suppress mutations of SIR4. RNA blot analysis suggests that this suppression is not due to transcriptional regulation of SIR3 by SIR4; nor does any SIR4 gene transcriptionally regulate another SIR gene. Interestingly, a truncated SIR4 gene disrupts regulation of the silent mating type loci. We propose that interaction of at least the SIR3 and SIR4 gene products is involved in regulation of the silent mating type genes.