Recipient competence in F''lac matings of Escherichia coli K-12.

We studied recipient mating ability in the presence of excess F'lac donors. Ninety-five percent of recipients were able to receive F'lac in 30-min matings. Competition between an F'-lac donor and an F'lac traI donor, which mobilized a ColE1 derivative (pML2), showed that each recipient mated with an average of two to three donors in 30 min. Experiments in which the competing donor was added at different times showed that some competition occurred throughout the 30-min mating period, which suggested that aggregate formation was spread over this time.     

A statistical method for correlating tRNA sequence with amino acid specificity.

A statistical method for finding the nucleotide positions in tRNA sequences that correlate with amino acid specificity has been developed. The procedure involves finding the subset of nucleotide positions and groups of positions where the marginal density of one amino acid tRNA class does not overlap that of any other amino acid class. The procedure is an application of a statistical method known as the Expectation Maximization algorithm.     

Coordinate regulation of ribosomal protein mRNA level in regenerating rat liver. Study with the corresponding mouse cloned cDNAs.

Cloned mouse ribosomal protein (rp) cDNAs exhibit extensive homology with the corresponding rat sequences. The size of the rp-mRNAs and complexity of the rp-genes are very similar in the two species. Using the mouse rp-recombinant DNAs we find that the relative abundance of rat L7, L13, L18, L30, L32/33 and S16 mRNAs increases after partial hepatectomy. Their maximal level is about twice that of normal rat liver, and is achieved 12-18 h after the operation, while the relative abundance of albumin mRNA decreases to half the normal values 12 h after partial hepatectomy. This concomitant increase in the relative content of these rp-mRNAs indicates coordinate regulation of their level in the rat. The dissimilar behavior of L10 and L19 rp-mRNA suggests additional control mechanisms of rp-mRNA levels in the regenerating rat liver.