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F W Studier

Publications and source records attributed to F W Studier.

84 records · Page 5Linked to original sources
PubMed1973

T7 early RNAs and Escherichia coli ribosomal RNAs are cut from large precursor RNAs in vivo by ribonuclease 3.

The early region of T7 DNA is transcribed as a single unit in a Ribonuclease III-deficient E. coli strain to produce large molecules essentially identical to those produced in vitro by E. coli RNA polymerase. As with the in vitro RNAs, these molecules are cut by purified RNase III in vitro to produce the messenger RNAs normally observed in vivo. Thus, the normal pathway for producing the T7 early messenger RNAs in vivo appears to involve endonucleolytic cleavage by RNase III. The uninfected RNase III-deficient strain contains several RNAs not observed in the parent strain. Patterns of labeling in vivo suggest that the largest of these RNAs, about 1.8 x 10(6) daltons, may be a precursor to the 16S and 23S ribosomal RNAs. When this large molecule is treated in vitro with purified RNase III, molecules the size of precursor 16S and 23S ribosomal RNAs are released; hybridization competition experiments also indicate that the 1.8 x 10(6) dalton RNA does indeed represent ribosomal RNA. Thus, RNase III cleavage seems to be part of the normal pathway for producing at least the 16S and 23S ribosomal RNAs in vivo. Several smaller molecules are also released from the 1.8 x 10(6) dalton RNA by RNase III, but it is not yet established whether any of these contain 5S RNA sequences.

Centrifugation, Density Gradient↗
PubMed1973

T7 early RNAs are generated by site-specific cleavages.

Transcription of T7 DNA by purified Escherichia coli RNA polymerase without added factors produces long RNA molecules that begin near the left end of T7 DNA and terminate at the end of the early region. An endonuclease has been isolated from uninfected E. coli that cleaves these long RNAs at five specific sites to generate RNA molecules essentially the same as the early T7 RNAs observed in vivo. This sizing factor, which may be RNase III, can act during or after RNA synthesis. Synthesis of early RNA chains has been shown to start at three strong initiators, spaced about 150-200 base-pairs apart near the left end of T7 DNA. Thus, the five cleavages by sizing factor generate the five early messenger RNAs of T7 plus three overlapping RNAs from the promoter region. RNA chains that are started at two of the strong initiators begin with A; those started at the third begin with G. A few minor initiators have also been observed, from which only short chains seem to be synthesized. Their locations in T7 DNA have not been mapped. Rho factor does not appear to be needed to generate any of these early T7 RNAs.

Adenosine Triphosphate↗
PubMed1972

Bacteriophage T7.

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Amino Acids↗
PubMed1970

The structural gene for a T7 endonuclease essential for phage DNA synthesis.

Infection of Escherichia coli with bacteriophage T7 results in the appearance of an endonuclease activity capable of hydrolyzing both double-and single-stranded DNA. Treatment with chloramphenicol prevents the induction of the endonuclease. Amber mutants of phage T7 defective in gene 3 are unable to produce the enzyme after infection of the nonpermissive host, and mutants that produce a heat-labile endonuclease were found, indicating that this gene is the structural gene for the enzyme. Gene 3 mutants synthesize only a limited amount of DNA. In addition, they are defective in carrying out the degradation of host DNA, suggesting that the gene 3 endonuclease is involved in this function.

Centrifugation, Density Gradient↗