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Biomedical subjects

M Yarus

Publications and source records attributed to M Yarus.

113 records · Page 7Linked to original sources
PubMed1967

Ultraviolet sensitivity of the biological activity of phi-X-174 virus, single-stranded DNA, and RF DNA.

Action spectra for inactivation of varphiX virus, free varphiX single-stranded DNA, and double-stranded varphiX DNA (RF) have been measured using light of wavelength 225-302 mmu. The sensitivity of RF has been determined using bacterial hosts both capable and incapable of reactivation of UV damage. The inactivation of varphiX virus is due, at all wavelengths, to damage to its DNA; it appears that, below 240 mmu, energy absorbed by viral structural protein may inactivate the viral DNA. The variation of the probability of inactivation by an absorbed quantum (quantum yield) with wavelength, in the case of free-single-stranded varphiX DNA, suggests that energy absorbed by pyrimidine residues is more likely to yield inactivation than absorption by purines. This implies that energy transfer is not so extensive as to make all absorbed energy available to pyrimidines.

Coliphages↗
PubMedDate not supplied

How mitochondria redefine the code.

Annotated, complete DNA sequences are available for 213 mitochondrial genomes from 132 species. These provide an extensive sample of evolutionary adjustment of codon usage and meaning spanning the history of this organelle. Because most known coding changes are mitochondrial, such data bear on the general mechanism of codon reassignment. Coding changes have been attributed variously to loss of codons due to changes in directional mutation affecting the genome GC content (Osawa and Jukes 1988), to pressure to reduce the number of mitochondrial tRNAs to minimize the genome size (Anderson and Kurland 1991), and to the existence of transitional coding mechanisms in which translation is ambiguous (Schultz and Yarus 1994a). We find that a succession of such steps explains existing reassignments well. In particular, (1) Genomic variation in the prevalence of a codon's third-position nucleotide predicts relative mitochondrial codon usage well, though GC content does not. This is because A and T, and G and C, are uncorrelated in mitochondrial genomes. (2) Codons predicted to reach zero usage (disappear) do so more often than expected by chance, and codons that do disappear are disproportionately likely to be reassigned. However, codons predicted to disappear are not significantly more likely to be reassigned. Therefore, low codon frequencies can be related to codon reassignment, but appear to be neither necessary nor sufficient for reassignment. (3) Changes in the genetic code are not more likely to accompany smaller numbers of tRNA genes and are not more frequent in smaller genomes. Thus, mitochondrial codons are not reassigned during demonstrable selection for decreased genome size. Instead, the data suggest that both codon disappearance and codon reassignment depend on at least one other event. This mitochondrial event (leading to reassignment) occurs more frequently when a codon has disappeared, and produces only a small subset of possible reassignments. We suggest that coding ambiguity, the extension of a tRNA's decoding capacity beyond its original set of codons, is the second event. Ambiguity can act alone but often acts in concert with codon disappearance, which promotes codon reassignment.

Base Composition↗
PubMedDate not supplied

[Interaction of RNA with phospholipid membranes].

RNAs binding with liposomes under near physiological conditions were obtained by molecular selection. Structural analysis showed that the RNAs could form complexes owing to complementary sequences located in loops. Oligomerization of the RNAs selected was experimentally confirmed. The results and published data testified that formation of high-molecular-weight complexes is a major mechanism increasing the RNA affinity for phospholipid membranes. The role of RNA-membrane interactions in early evolution is discussed in terms of the RNA world hypothesis.

Base Sequence↗