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F Imamoto

Publications and source records attributed to F Imamoto.

At least 109 records · Page 6Linked to original sources
PubMed1976

Initial trp operon sequence in Escherichia coli is transcribed without coupling to translation.

The transcription of the "leader" region (Bronson et al., 1973) of the trp operon in Escherichia coli was studied in normal mutants which delete most of the operator-distal region of the operon [a deletion strain (trp OAEG) retaining only about one third of the "leader" region and two deletion strains (trpOAE14 and trpOAE2) retaining the whole "leader" region and an initial portion of the trpE], as well as in a strain with an intact trp operon, but with a temperature-sensitive lesion in ribosomal protein factor EFTs (strain HAK88). In these deletion mutants, mRNA molecules corresponding to the "leader" region were detected as most of the trp-specific mRNA. Less inhibition of transcription, of the promoter-proximal portion of the trp "leader" region than that of more distal genes of the operon, was found in chloramphenicol-treated cells of strain trpOAE14. It was also observed that transcription of the initial one third portion of the "leader" region was not repressed by tryptophan in strains trpOAE6 and trp OAE14. A similar effect of a translation block on transcription of the distal part of the "leader" region was observed with strain HAK88 at the nonpermissive temperature. In sedimentation analysis of polyribosomes containing the trp mRNA molecules from the deletion mutants, trp mRNA from strain trpOAE14 was found in monosomes and small polyribosomes, whereas the majority of the trp mRNA from strain trpOAE6 was found joined to a single ribosome or ribosomal subunit. These results suggest that ribosomes bind in vivo to a site(s) located in the middle of the "leader" mRNA sequence, and that the initial transcription of the trp operon does not require any connection to functional translational machinery, while continuation of RNA synthesis beyond a first ribosome binding site seems indispensably coupled to ribosome function.

DNA, Bacterial↗
PubMed1976

Dual transcription of the tryptophan operon translocated into the early region of gamma.

The mode of transcription of the trp operon translocated into the early region of bacteriophage lambda was studied. Synthesis of trp mRNA specific for the translocated trp operon in lambdatrp phage was assayed after infecting a bacteria carrying a deletion mutant (trpAE1), which lacks the whole trp operon but retains a trp regulator gene (trpR). To determine trp mRNA from lambdatrp, phage phi80trp was employed as a source of DNA in hybridization assays. trp mRNA synthesis by lambdatrpE-A, which possesses the intact trp operon, was found to be only partially repressed by fully activated trp repressor in strain trpAE1. On the other hand, trp mRNA synthesis by lambdatrpE-A in strain trpAE1 (lambda), lysogenic for lambda and therefore possessing lambda repressor, was completely repressed when the trp repressor was fully activated by the addition of excess tryptophan. trp mRNA synthesis from the trp operon segment in lambdatrpBA, which carries the trpA and trpB genes but does not possess the trp promoter and operator, was not affected at all by trp repressor but was regulated completely by lambda repressor. The possibility was excluded that the trp mRNA whose synthesis is insensitive to trp repressor is anti-messenger originating from the nonsense(r)-strand of the translocated trp operon of lambdatrp. These observations led to the conclusion that transcription of the translocated trp operon in lambdatrpE-A consists of two types; one is initiated at the trp promoter and is controlled by the trp repressor, another is initiated by a lambda promoter (PL of gene N) and is controlled by the lambda repressor.

Chromosome Aberrations↗
PubMed1976

Differential sensitivity to antibiotics of trp mRNA synthesis originating at the trp promoter and the lambda promoter.

Transcription of the Escherichia coli trp operon translocated into the early region of bacteriophage lambda can occur under the control of either of two promoters, the trp promoter on the lambda promoter (OL of N gene). (Imamato, F. and Tani, S. (1972) Nat. New Biol. 240, 172-175 and Ihara S. and Imamoto, F. (1976) Biochim. Biophys. Acta 432, 199-211). Trp mRNA synthesis originating at the trp promoter stopped when translation was blocked by chloramphenicol tetracycline erythromycin or puromycin. In contrast, trp mRNA synthesis originating at the lambda promoter was not affected by antibiotic action. This probably is a reflection of the properties of the "immediate early" class of genes of lambda, whose transcription in initiated at the PL. promoter and is not inhibited by the antibiotic. The inference is strengthened by comparable results with phage lambdatrpE-A (carrying an intact tro operon) and lambdatrpBA (carrying the operator-distal two genes but missing the trp promoter and operator). Thus it seems that either the promoter or other gene(s) located at the beginning of the operon, either at polymerase addition or because of some feature of the transcript, can determine a requirement for "coupling" of RNA polymerase to the translational machinery in vivo.

Chloramphenicol↗
PubMed1975

Polarity in segments of the Escherichia coli trp operon with deleted intraoperonic translational initiation signals.

The effect of deletion of the operator-distal genes of the trp operon, including the trpE-trpD intercistronic punctuation point, on the degree of transcriptional polarity (in this case the effect of a nonsense mutation on the level of mRNA from the distal part of the very gene where the mutation is located) was investigated. Double mutants which contain a nonsense mutation and a deletion in trpE were constructed, and the degree of transcriptional polarity was estimated by the decrease in messenger RNA for the operator-distal trpE beyond the nonsense mutation, as well as by the production of truncated messenger RNA for the region of trpE proximal to the nonsense mutation. The content of mRNA of operator-distal trpE and the size of the mRNA of operator-proximal trpE of the double mutants show that transcriptional polarity is not relaxed as a function of distance of the nonsense mutation from the operator-distal end of the trpE segment (at which the subsequent high efficiency translational initiation signal has been deleted). These findings are consistent with the conclusion that the degree of polarity depends on the distance of the nonsense mutation from the subsequent translation initiation signal, but not on its distance from the operator-distal end, including possible translational or transcriptional termination signals.

Escherichia coli↗