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S L Bektesh

Publications and source records attributed to S L Bektesh.

6 recordsLinked to original sources
PubMed1991

Comparison and analysis of the nucleotide sequences of pilin genes from Haemophilus influenzae type b strains Eagan and M43.

Previous studies have demonstrated antigenic differences among the pili expressed by various strains of Haemophilus influenzae type b (Hib). In order to understand the molecular basis for these differences, the structural gene for pilin was cloned from Hib strain Eagan (p+) and the nucleotide sequence was compared to those of strains M43 (p+) and 770235 b0f+, which had been previously determined. The pilin gene of Hib strain Eagan (p+) had a 648-bp open reading frame that encoded a 20-amino-acid leader sequence followed by the 196 amino acids found in mature pilin. The translated sequence was three amino acids larger than pilins of strains M43 (p+) and 770235 b0f+ and was 78% identical and 95% homologous when conservative amino acid substitutions were considered. Differences between the amino acid sequences were not localized to any one region but rather were distributed throughout the proteins. Comparison of protein hydrophilicity profiles showed several hydrophilic regions with sequences that were conserved between strain Eagan (p+) and pilins of other Hib strains, and these regions represent potentially conserved antigenic domains. Southern blot analyses using an intragenic probe from the pilin gene of strain Eagan (p+) showed that the pilin gene was conserved among all type b and nontypeable strains of H. influenzae examined, and only a single copy was present in these strains. Homologous genes were not present in the phylogenetically related species Pasteurella multocida, Pasteurella haemolytica, and Actinobacillus pleuropneumoniae. These data indicate that the pilin gene was highly conserved among different strains of H. influenzae and that small differences in the pilin amino acid sequences account for the observed antigenic differences of assembled pili from these strains.

Amino Acid Sequence↗
PubMed1985

Interaction of rho factor with bacteriophage lambda cro gene transcripts.

Rho protein is responsible for termination of transcription of the cro gene of bacteriophage lambda. Since rho is known to interact with the RNA whose synthesis is being terminated, we measured the specificity and strength of binding of rho to isolated cro transcripts, using a nitrocellulose filter retention assay. The association constant (K alpha) for the binding of rho to a 372-nucleotide cro transcript was determined to be 7 +/- 2 X 10(8) M-1 at 37 degrees C and about 20-fold less at 4 degrees C. Although NTP cleavage is required for rho activity, the presence of ATP did not alter the K alpha. Rho bound less tightly (K alpha less than 10(8) M-1) to partial cro transcripts smaller than 290 nucleotides and had very little affinity (K alpha less than 10(6) M-1) for lambda 4 S RNA, lambda 6 S RNA, and partial cro transcripts smaller than 160 nucleotides. In contrast, cro transcripts as short as 100 nucleotides bound if guanosine residues were replaced with inosine. In addition, rho bound readily to 3' fragments of cro RNA that had 85 or more residues. A common feature of the RNA molecules that bind tightly to rho protein is that they have a stretch of at least 85 nucleotides with relatively few (less than 14%) guanosine residues. Such a segment is thus likely to be largely single-stranded. These results suggest that the binding of rho to lambda cro mRNA is dependent on a 3' terminal segment that has those properties.

Bacteriophage lambda↗
PubMed1984

Replication, integration and expression of exogenous DNA injected into fertilized eggs of Xenopus laevis.

We have analyzed the fate of circular and linear DNA molecules following microinjection into the cytoplasm of fertilized eggs of Xenopus laevis. Recombinant plasmids containing sea urchin histone genes (pSp 102), Drosophila ADH genes (sAC-1), and SV40 (SV2 CAT) replicate during the development of the injected frog embryo. In contrast, pBR322 either as monomers or multimers does not appear to replicate as efficiently. Generally, injected circular DNAs were not detectable by the gastrula stage of development, although there were several examples in which these molecules persisted until larval stages. In 90% of the cases, injected linear DNAs persisted as discrete molecules into early embryonic stages. A portion of the DNA sequences complementary to injected linear and circular molecules was detected comigrating with the high-molecular-weight cellular frog DNA (48 kb or larger) from mid-cleavage stages onward. Restriction enzyme analysis of DNA from injected embryos suggested some copies of the injected DNAs were integrated into the frog genome. This occurred in about 10%-30% of the cases of injected circular DNA and approximately 60%-70% of the cases of injected linear DNA. We were able to rescue circular plasmids from the injected blastulae by retransforming Escherichia coli. Restriction enzyme analysis of this DNA suggested that the majority of injected circular DNAs were not modified following replication in the frog embryo. The DNA of Xenopus embryos was highly methylated. On the other hand, injected DNA sequences were not methylated de novo even after many replication cycles in the frog embryo. Ribonucleic acid (RNA) transcripts from the injected DNAs were detectable by the late blastula stage of development.

Animals↗
PubMed1981

Inhibition of the action of Escherichia coli transcription termination protein rho by poly(C) and heparin.

Poly(C) and heparin at low concentrations (1 microgram/ml) prevent the RNA synthesis termination protein rho from functioning during the biosynthesis of RNA from bacteriophage T7 DNA catalyzed by Escherichia coli RNA polymerase. Both of these polyanions inhibit the binding of rho to isolated T7 RNA. Heparin also inhibits rho ATPase when isolated RNA transcripts are used as cofactors. It is concluded that the polyanions inhibit termination by binding to the site on rho that is normally used for the initial interaction with a nascent RNA transcript in the rho-mediated release of RNA. Since one of the inhibitors, poly(C), is itself a potent activator for rho ATPase, it is also concluded that the ATP hydrolysis step that is required for rho termination has to be coupled to an action of rho on the RNA molecule to be released from the transcription complex.

Adenosine Triphosphatases↗
PubMed1980

A rho-recognition site on phage lambda cro-gene mRNA.

The synthesis of RNA catalysed by RNA polymerase from Escherichia coli is terminated at specific sites on DNA templates through the action of a multimeric basic protein known as rho (refs 1, 2). Three lines of evidence suggest that an interactions of rho with the nascent RNA is important for this termination. First, rho binds strongly to RNA; second, rho expresses an RNA-dependent ATPase activity which is essential for termination; third, RNA polymerase does not terminate RNA synthesis at rho-dependent sites when the nascent RNA is digested by ribonuclease during transcription. From the fact that certain RNAs, particularly single-stranded, pyrimidine-rich polymers containing at least 10% cytidylate residues, are more effective than other RNAs at promoting rho-ATPase, it has been proposed that rho recognises specific sites oion on a mRNA transcribed from bacteriophage lambda DNA.

Bacteriophage lambda↗