Peptide bond formation stimulated by protein synthesis factor EF-P depends on the aminoacyl moiety of the acceptor.

Elongation factor EF-P is a soluble protein that stimulates peptide bond synthesis catalyzed by the 50-S ribosomal subunit. This factor was previously identified and characterized based on its ability to promote the synthesis of formylmethionine-puromycin. In the present work, we tested the ability of EF-P to promote peptide bond synthesis between ribosome-bound fMet-tRNA and several analogues of the 3' terminus of aminoacyl-tRNA, i.e. the cytidylyl(3'-5')-[2'(3')-O-L-aminoacyladenosines]. EF-P promoted synthesis to the greatest extent with certain acceptors which were otherwise inefficient in the peptidyl transferase reaction. This activity of EF-P could not be replaced by the other soluble proteins known to be involved in polypeptide synthesis, such as EF-Tu, EF-Ts and EF-G. One role of EF-P in protein synthesis may be to allow peptide bond synthesis to occur more efficiently with some aminoacyl-tRNAs that are poor acceptors for the ribosomal peptidyl transferase.     

Heritable determinants of left-right bias in the rat

The offspring of matings of rats having opposite or same-sided turning biases were tested for turning biases as adults and the degree of similarity to the parents' biases assessed. There were significant and equivalent tendencies for the male offspring to have the same bias as the male parent and the opposite bias as the female parent. Although, overall, female offspring were distributed randomly with respect to the parents' biases, a significant tendency for female offspring to have biases opposite those of the female parent was apparent in litters having more males than females. Based on reports indicating a relationship between the sex ratio of a litter and levels of testosterone in female fetuses, it was suggested that $\text{in utero}$ exposure to testosterone reverses the coding of a heritable female influence and induces a tendency for the offspring to have biases opposite those of the female parent. The origins of sidedness in the rat appear to involve a complex interaction between heredity and hormones.     

Effect of Wound Shock on Protein Synthesis in Leaves of C3 and C4 Plants

Wound stress causes an initial decrease in the uptake and subsequentincorporation of radiolabelled methionine in leaves of C₃ (peanutand soybean) and C₄ (sorghum and maize) plants. A four-hourincubation of excised leaves at 25C permits them to recoverfrom wounding and thereby facilitates monitoring of changesin protein synthesis caused by heat shock or other types ofenvironmental stress. (Received December 7, 1992; Accepted February 16, 1993)