2'-Versus 3'-OH specificity in tRNA aminoacylation. Further support for the "secondary cognition" proposal.

Purified Escherichia coli tRNAAla and tRNALys were each converted to modified species terminating in 2'- and 3'-deoxyadenosine. The modified species were tested as substrates for activation by their cognate aminoacyl-tRNA synthetases and for misacylation with phenylalanine by yeast phenylalanyl-tRNA synthetase. E. coli alanyl- and lysyl-tRNA synthetases normally aminoacylate their cognate tRNA's exclusively on the 3'-OH group, while yeast phenylalanyl-tRNA synthetase utilizes only the 2' position on its own tRNA. Therefore, the finding that the phenylalanyl-tRNA synthetase activated only those modified tRNAAla and tRNALys species terminating in 3'-deoxyadenosine indicated that the position of aminoacylation in this case was specified entirely by the enzyme, an observation relevant to the more general problem of the reason(s) for using a particular site for aminoacylation and maintaining positional specificity during evolution. Initial velocity studies were carried out using E. coli tRNAAla and both alanyl- and phenylalanyl-tRNA synthetases. As noted in other cases, activation of the modified and unmodified tRNA's had essentially the same associated Km values, but in each case the Vmax determined for the modified tRNA was smaller.     

Variation in the growth of the preweaning Syrian hamster (Cricetus auratus)

An assessment of the growth rate spectrum based on a longitudinal weight study of golden hamsters was undertaken over the preweaning period. The period covered 23 days with data probes at 24-hourly intervals and encompassed 16 litters providing a birth number of 120 young and a weaning survival number of 82. Subsequent analysis directed initially at the pooled or averaged data showed sex differences with males gaining weight faster than females. Further analysis showed the total period to have three definitive break-points and therefore four phases of growth activity. The segmented linear regression line calculations showed that the phasic duration of males in the second and third phases were two days later than the females. Following data-analysis adjustments and taken into account aberrations of the sample, final indications pointed to the preweaning hamster growth spectrum as quadrophasic, exhibiting a stable first phase, a second and third phase terminating earlier in females and a final weaning weight being heavier in males. The growth curves demonstrated a 'U' shaped outline and formed an integral part of hamster preweaning precocity.     

Increase in testicular androgen receptor during sexual maturation in the rat

Androgen receptor concentration was measured by exchange with 3H-dimethylnortestosterone (DMNT) in cytosol and nuclear extracts from testes of rats 15-90 days of age. Dissociation kinetics verified the necessity of an extended incubation (86 h) for maximum exchange at 4 degrees C. Nuclear androgen receptor concentration per mg DNA decreased between 15 and 25 days of age, from 375 to 146 fmol per mg DNA, then increased to 584 fmol per mg DNA at 90 days. Testicular receptor content also increased between 25 and 90 days of age. Cytosol receptor concentration patterns were similar to nuclear androgen receptor patterns. The affinity of the receptor for the ligand did not change with age (mean Kd = 0.88 nM). No significant difference in androgen receptor concentration per cell was detected between cultured peritubular cells from animals 25 and 45 days of age. Androgen receptor concentrations in freshly isolated peritubular cells could not be determined. There also was no difference in receptor concentration per cell in a Leydig cell-enriched fraction from animals between 25 and 45 days of age. Although androgen receptor concentrations per Sertoli cell increased between 15 and 35 days of age, the increase in Leydig cell number over the same period probably accounted for approximately 75% of the increase in receptor per testis between 25 and 45 days of age.