The yeast alpha 1 and MCM1 proteins bind a single strand of their duplex DNA recognition site

Tunable cell differentiation via reprogrammed mating-type switching

This study introduces a synthetic biology approach that reprograms the yeast mating-type switching mechanism for tunable cell differentiation, facilitating synthetic microbial consortia formation and cooperativity. The underlying mechanism was engineered into a genetic logic gate capable of inducing asymmetric sexual differentiation within a haploid yeast population, resulting in a consortium characterized by mating-type heterogeneity and tunable population composition. The utility of this approach in microbial consortia cooperativity was demonstrated through the sequential conversion of xylan into xylose, employing haploids of opposite mating types each expressing a different enzyme of the xylanolytic pathway. This strategy provides a versatile framework for producing and fine-tuning functionally heterogeneous yet isogenic yeast consortia, furthering the advancement of microbial consortia cooperativity and offering additional avenues for biotechnological applications.

Characterization of a polypyrimidine/polypurine tract in the promoter of the gene for chicken malic enzyme

Starvation inhibits and refeeding stimulates transcription of the malic enzyme gene in chick liver. DNA between -320 and +72 base pairs (bp) is DNase I-hypersensitive in hepatic nuclei from fed but not starved chicks (Ma, X. J., and Goodridge, A. G. (1992) Nucleic Acids Res. 20, 4997-5002). A polypyrimidine/polypurine (PPY/PPU) tract lies within the DNase I-hypersensitive region. In hepatocytes transiently transfected with plasmids containing triiodothyronine response elements and a minimal promoter from the malic enzyme gene linked to the chloramphenicol acetyltransferase gene, deletion of the PPY/PPU tract inhibited chloramphenicol acetyltransferase activity by about 90% with or without triiodothyronine. Fine mapping of S1 nuclease-sensitive sites suggests that the PPY/PPU tract can assume different isoforms of non-B-DNA, some of which may be triplex structures. The PPY/PPU tract contains specific binding sites for single- and double-stranded DNA binding proteins and, with 8 bp 3' of the tract, can function as a promoter. A (CT)7 repeat binds single-stranded DNA-binding protein and is essential for promoter activity. Two C-rich elements bind single-stranded DNA-binding proteins and may mediate inhibition of promoter function. The single- and double-stranded DNA-binding proteins that interact with the PPY/PPU tract may regulate transcription of the malic enzyme gene.

Molecular mechanisms of cell-type determination in budding yeast

Studies of cell-type determination in the yeast Saccharomyces cerevisiae have revealed a regulatory network of proteins that are highly conserved in evolutionary terms. In the past few years, genetic, biochemical, and structural approaches have shown what many of these components do, how they fit together, and how they cooperate to regulate the expression of many different target genes.

The 30-kDa protein binding to the "initiator" of the baculovirus polyhedrin promoter also binds specifically to the coding strand

We previously reported the purification and characterization of the polyhedrin promoter-binding protein (PPBP), an unusual DNA-binding protein that interacts with transcriptionally important motifs of the baculovirus polyhedrin gene promoter (S. Burma, B. Mukherjee, A. Jain, S. Habib, and S.E. Hasnain, J. Biol. Chem. (1994) 269, 2750-2757. PPBP also exhibits a sequence-specific single-stranded DNA-binding activity. Gel retardations and competition analyses with double- and single-stranded oligonucleotides indicated that PPBP binds the coding strand and not the noncoding strand of the promoter. This was further confirmed by UV cross-linking and Southwestern blotting experiments. Gel retardations with mutated oligonucleotides indicated that both dsDNA and ssDNA binding involve common AATA-AATAAGTATT motifs. However, ssDNA binding is dependent upon ionic interactions unlike dsDNA binding, which is mainly through nonionic interactions. The affinity of PPBP for the coding strand appears to be higher than that for duplex promoter DNA. Interestingly, the PPBP-coding strand complex has a longer half-life (approximately 60 min) than the PPBP-duplex promoter complex (approximately 15 min). PPBP represents a unique example of an "initiator" promoter-binding protein with dual dsDNA and ssDNA binding activities, and this reconciles very well with the unusual binding characteristics displayed by it. The formation of the PPBP-coding strand complex in vivo may be a crucial step for the exceptionally high and repeated rounds of transcriptional activity of the baculovirus polyhedrin gene promoter.

Single-stranded DNA-protein binding in the procyclic acidic repetitive protein (PARP) promoter of Trypanosoma brucei

We performed gel retardation analyses of DNA-protein interactions using DNA from the procyclic acidic repetitive protein (PARP) promoter of the protozoan parasite Trypanosoma brucei. The PARP genes of Trypanosoma brucei are transcribed in an alpha-amanitin resistant manner, and it has been proposed that RNA polymerase I, rather than RNA polymerase II, transcribes the PARP genes. Double-stranded restriction fragments containing the essential PARP-promoter regions bound only sequence-nonspecific nuclear factors, even though protein factors that bind specifically to double-stranded DNA from the snRNA U2 promoter were present in the extracts. In contrast, single-stranded DNA-binding proteins bound with high affinity, nucleotide-sequence and strand-specificity to the -69/-55 element and the coding and non-coding strands of the -37/-11 element.