The unknown modified nucleotide G*, isolated from both Schizosaccharomyces pombe and Torulopsis utilis initiator tRNAs(Met), has been identified as an O-ribosyl-(1"----2')-guanosine-5"-phosphate, called Gr(p), by means of HPLC, UV-absorption, mass spectrometry and periodate oxidation procedures. By comparison with the previously published structure of Ar(p) isolated from Saccharomyces cerevisia...

Selection of a translation initiation site is thought to be determined by relative proximity to the 5' end and sequence context of a potential initiator codon. These guidelines seem insufficient to explain translation of the Drosophila E74A mRNA, whose 5' untranslated region is exceptionally long (1.8 kb) and contains many AUG triplets preceding the long open reading frame. In an effort to unde...

The replicon of the low copy number plasmid pSC101 has an obligatory requirement for the dnaA initiator protein of Escherichia coli as well as a plasmid-encoded initiator protein. We have identified the cistron of the plasmid-encoded initiator by DNA sequence analysis. Fusion of the initiator cistron with the lacZ gene of E. coli yielded a fusion protein of approximately equal to 150 kilodalton...

Of all tRNAs, initiator tRNA is unique in its ability to start protein synthesis by directly binding the ribosomal P-site. This ability is believed to derive from the almost universal presence of three consecutive G-C base (3G-C) pairs in the anticodon stem of initiator tRNA. Consistent with the hypothesis, a plasmid-borne initiator tRNA with one, two, or all 3G-C pairs mutated displays negligi...

Initiator tRNAs are used exclusively for initiation of protein synthesis and not for elongation. We show that both Escherichia coli and eukaryotic initiator tRNAs have negative determinants, at the same positions, that block their activity in elongation. The primary negative determinant in E. coli initiator tRNA is the C1xA72 mismatch at the end of the acceptor stem. The primary negative determ...

A new protocol for carcinogenesis in rat liver is described in order that confirmatory experiments might be undertaken concurrently. The basic protocol, designated IPI (initiator + promoter + initiator), is presented in several alternative forms, including the possible use of X-irradiation as the initiator. The rationale is discussed in terms of the two-hit somatic mutation theory of Armitage a...

Commercial initiator – 2,2-dimethoxy-2-phenyl acetophenone (Irgacure 651, Ciba, Switzerland) was introduced to poly(methyl methacrylate) (PMMA) matrix to enhance the polymer degradation. Two types of thin polymeric films (PMMA and PMMA+5% Irgacure) were UV-irradiated in laboratory conditions (Xenon lamp, air atmosphere, room temperature). The photochemical changes in pure PMMA and PMMA doped wi...

In prokaryotes, many of the physical mechanisms governing the process of initiating DNA replication are now emerging. For example, certain organizational features of origins, such as the use of repetitive sequence elements for initiator-binding sites, are found throughout bacteria and many archaea. Common themes in the regulation of initiation, including origin sequestration by trans-acting fac...