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D Mascarenhas

Publications and source records attributed to D Mascarenhas.

23 records · Page 2Linked to original sources
PubMed1983

Retroregulation: control of integrase expression by the b2 region of bacteriophages lambda and 434.

Genetic fusions constructed by a combination of in vivo and in vitro techniques have been used to investigate the cis-regulatory role of a 250-base-pair segment of b2 DNA in the expression of int transcripts originating from three different promoters PI, PL, and PTRP. It has been established that (a) the PI and PTRP transcripts, which produce functional int protein, are efficiently terminated by the b2 segment, (b) in the same test system, the PL transcript, which does not result in functional integrase, is not terminated by the b2 segment, (c) this b2 (sib) effect does not depend on genes lying between int and N on the phage genome, (d) the sib effect is also observed with the b2 DNA of phage 434, which resembles that of lambda between -197 and att but diverges radically from it to the left of base -197.

Bacteriophage lambda↗
PubMed1982

Probing cII and himA action at the integrase promoter pi of bacteriophage lambda.

Plasmids were constructed to supply cII-coded protein for activation of the phage promoter pI. Using a fusion which expresses lacZ from pI. We can accurately follow activation of pI without having to assay int activity in vivo. A large excess of cII protein compared to a normal lytic infection stimulates lacZ expression about 10-fold over the basal level. The int-c226 constitutive allele of pI is not further activated by cII even though its level of lacZ expression is less than the maximal cII-activated expression from wild type pI. A himA-deleted strain also shows activation, demonstrating that there is no absolute requirement for the himA gene product for cII-stimulated transcription at pI.

Bacteriophage lambda↗
PubMed1981

DNA sequence of the att region of coliphage 434.

Phages lambda and 434 are related phages that insert at the same site on the Escherichia coli chromosome. A 5.9-kb SalI-BamHI fragment derived from phage 434 was shown to hybridize to a 0.5-kb probe carrying attP-lambda. A 0.8-kb Bam HI-TaqI fragment subcloned into pBR327 was used for sequencing. The sequence of the 500 bp around the insertion site is given here, Comparison of the lambda and 434 sequence shows that the following regions are conserved: the coding sequence for the integrase protein (only 162 bp have been sequenced corresponding to the carboxy terminus), the 15-bp common core at the insertion site, and the three integrase-binding sites flanking the insertion site. The lambda and 434 sequences diverge radically to the left of base-197, suggesting that DNA to the left of that point plays no specific role in insertion or its regulation.

Attachment Sites, Microbiological↗
PubMed1980

DNA sequence of regulatory region for integration gene of bacteriophage lambda.

The cII and cIII proteins specified by bacteriophage lambda direct the lysogenic response to infection through the coordinate establishment of repression and integration of the viral DNA. The regulatory activity of cII/cIII involves positive regulation of two promoter sites: the p(E) promoter, turning on expression of the cI protein that maintains lysogeny, and the p(I) promoter, activating synthesis of the Int protein for integrative recombination. Regulation of the p(I) promoter provides for differential expression of the Int protein with respect to the excision-specific Xis protein from the closely linked int and xis genes. We have determined the DNA sequence of the p(I) promoter region for wild-type lambda DNA and for two classes of mutations: intc mutations, which result in a high rate of Int synthesis in the absence of cII, and deletion mutations, some of which eliminate cII-activated expression of the int gene. We find a sequence with considerable homology (11 of 15 bases) to a "typical" (computer-generated) promoter sequence, adjacent to a region with striking homology (11 of 14 bases) to part of the p(E) promoter region. This presumed p(I) sequence overlaps the start of the xis gene and includes the site of two intc point mutations. A cII-insensitive xis(+) deletion partially removes the proposed p(I) sequence; a deletion that leaves the p(I) sequence intact but terminates 21 bases upstream does not interfere with cII activation of the int gene. From our results and the analysis of the p(E) region, we suggest that cII acts in the promoter -35 recognition region to facilitate binding by RNA polymerase at the -10 interaction region. Differential expression of the int and xis genes results because the p(I) transcript lacks the initiation codon for Xis protein synthesis.

Bacteriophage lambda↗