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N F Lowndes

Publications and source records attributed to N F Lowndes.

26 records · Page 2Linked to original sources
PubMed1992

DNA synthesis control in yeast: an evolutionarily conserved mechanism for regulating DNA synthesis genes?

After yeast cells commit to the cell cycle in a process called START, genes required for DNA synthesis are expressed in late G1. Periodicity is mediated by a hexameric sequence, known as a MCB element, present in all DNA synthesis gene promoters. A complex that specifically binds MCBs has been identified. One polypeptide in the MCB complex is Swi6, a transcription factor that together with Swi4 also binds G1 cyclin promoters and participates in a positive feedback loop at START. The finding that Swi6 is directly involved in both START and DNA synthesis gene control suggest a model in which Swi6, activated through its participation in START, serves as the central transcription factor in coordinating late G1 gene expression. The mechanism may be conserved in all eukaryotic cells.

Animals↗
PubMed1991

Coordination of expression of DNA synthesis genes in budding yeast by a cell-cycle regulated trans factor.

All of the DNA synthesis genes of budding yeast examined so far are periodically expressed and hence under cell-cycle control (Table 1). Expression occurs near the G1/S phase boundary and the genes seem to be coordinately regulated (reviewed in ref. 4). The upstream promoter sequences of these genes have only a hexamer element, ACGCGT (an MluI restriction site), in common. Here we show that this hexamer is able to impart periodic expression to a heterologous gene and, significantly, this expression occurs coincidentally with that of CDC9, one of the DNA synthesis genes (Table 1). We have also identified a protein that binds specifically to these sequences in a similar periodic manner. These ACGCGT sequences and the transcription factor that binds to them therefore seem to be the elements controlling both the periodic expression and coordinate regulation of the DNA synthesis genes.

Cell Cycle↗
PubMed1991

The yeast DNA ligase gene CDC9 is controlled by six orientation specific upstream activating sequences that respond to cellular proliferation but which alone cannot mediate cell cycle regulation.

By fusing the CDC9 structural gene to the PGK upstream sequences and the CDC9 upstream to lacZ, we showed that the cell cycle expression of CDC9 is largely due to transcriptional regulation. To investigate the role of six ATGATT upstream repeats in CDC9 regulation, synthetic copies of the sequence were attached to a heterologous gene. The repeats stimulated transcription strongly and additively, but, unlike conventional yeast UAS elements, only when present in one orientation. Transcription driven by the repeats declines in cells held at START of the cell cycle or in stationary phase, as occurs with CDC9. However, the repeats by themselves cannot impart cell cycle regulation to a heterologous gene. CDC9 may therefore be controlled by an activating system operating through the repeats that is sensitive to cellular proliferation and a separate mechanism that governs the periodic expression in the cell cycle.

Base Sequence↗
PubMed1990

A short, highly repetitive element in intron -1 of the human c-Ha-ras gene acts as a block to transcriptional readthrough by a viral promoter.

We have identified a short, highly repetitive element within intron -1 of the human c-Ha-ras gene. This element was found to be transcribed in both orientations and to be homologous to heterogeneous nonpolyadenylated transcripts. The repetitive element blocked transcriptional readthrough from a strong upstream viral promoter but allowed unimpaired readthrough from the c-Has-ras promoter. We suggest that it may serve to prevent excessive transcription into the coding region of the gene under such circumstances as viral insertion.

Cell Line↗
PubMed1989

c-Ha-ras gene bidirectional promoter expressed in vitro: location and regulation.

Increased transcriptional activity of the c-Ha-ras gene product is correlated with induction of several important human tumor types. For this reason, we have investigated the nature of the c-Ha-ras promoter and the factors that regulate its expression. Using S1 and primer extension analysis of c-Ha-ras RNA from EJ cells, we have identified 18 initiation sites within an upstream exon (exon -1) whose 3' end (the donor splice site [D]) is located 1,105 base pairs (bp) upstream of the ATG codon. The furthest-upstream initiation site is located -191 bp relative to D, and the furthest downstream is located -16 bp relative to D. Transient expression assays, in which a series of mutants spanning this region were ligated to a promoterless chloramphenicol acetyltransferase vector, functionally confirmed the position and extent of this promoter. Mutational analysis further located a 47-bp element located between -243 and -196 relative to D that up-regulated transcriptional activity of the promoter region by 20- to 40-fold. This region contained both a GC box known to bind SP1 and a CCAAT box. Insertion of a simian virus 40 enhancer 5' to the promoter up-regulated transcription from each initiation site by approximately 10- to 20-fold. We have also localized, both by chloramphenicol acetyltransferase assay and by S1 analysis, a strong promoter operating in the direction opposite that of the gene and originating immediately 5' to the 47-bp regulatory region. The reverse promoter was found to have nine initiation sites between -248 and -278 relative to D.

Animals↗
PubMedDate not supplied

A role for Saccharomyces cerevisiae histone H2A in DNA repair.

Histone proteins associate with and compact eukaryotic nuclear DNA to form chromatin. The basic unit of chromatin is the nucleosome, which is made up of 146 base pairs of DNA wrapped around two of each of four core histones, H2A, H2B, H3 and H4. Chromatin structure and its regulation are important in transcription and DNA replication. We therefore thought that DNA-damage signalling and repair components might also modulate chromatin structure. Here we have characterized a conserved motif in the carboxy terminus of the core histone H2A from Saccharomyces cerevisiae that contains a consensus phosphorylation site for phosphatidylinositol-3-OH kinase related kinases (PIKKs). This motif is important for survival in the presence of agents that generate DNA double-strand breaks, and the phosphorylation of this motif in response to DNA damage is dependent on the PIKK family member Mec1. The motif is not necessary for Mec1-dependent cell-cycle or transcriptional responses to DNA damage, but is required for efficient DNA double-strand break repair by non-homologous end joining. In addition, the motif has a role in determining higher order chromatin structure. Thus, phosphorylation of a core histone in response to DNA damage may cause an alteration of chromatin structure that facilitates DNA repair.

Amino Acid Motifs↗