Partial gene duplication and posterior pituitary peptide

We have compiled the dipeptide frequencies in 100 known protein sequences. We suggest that dipeptides which occur with low frequencies can be used to locate proteins where partial gene duplication may have taken place. The 48 residue sequence of posterior pituitary peptide contains two Cys Trp pairs. The adjacent portions of the sequence are compatible with a partial gene duplication in the evolutionary history of posterior pituitary peptide.     

Aberrant DNA repair and enhanced mutagenesis following mutagen treatment of Chinese hamster Ade-C cells in a state of purine deprivation

Ade-C is a Chinese hamster ovary cell line auxotrophic for purines because of a mutation in the de novo synthetic pathway. We now show that, in the absence of exogenous hypoxanthine, replicative DNA synthesis is rapidly shut down. Various aspects of DNA repair have been studied in purine-starved cells. Incision, the first step of excision repair of UV damage, appears normal, as do the later steps, repair synthesis (demonstrated following chemical damage as well as UV-irradiation) and ligation. However, removal of UV-induced pyrimidine dimers is not detected, and it seems that the repair that occurs is aberrant. This behaviour is associated with an increase in cell killing by UV light, and a several-fold increase in the frequency of mutations induced by UV.     

Alkaline phosphatase and maltase activity in the embryonic chick intestine in culture. Influence of thyroxine and hydrocortisone.

In strips of duodenum from 14-day chick embryos explanted into defined medium, alkaline phosphatase (ALP) activity accumulated in the tissue at a faster rate than in vivo for about 48 hr, but failed to increase thereafter. The addition of thyroxine (T4) to the medium at 10^?8M or less both enhanced the early accumulation and elicited a very large increase in ALP activity comparable to that normally occurring during the last 2 days in ovo. Activity with phenylphosphate (PhP) was more strongly affected than that with β-glycerophosphate (βGP), so that the high $\text{PhP}\text{β}\text{GP}$ ratio attained in vivo at 18 days was reached after 24 hr in T4-supplemented medium. Hydrocortisone (HC) evoked APL activity only slightly above that in unsupplemented medium and only during the first 48 hr in culture, but it precociously elevated $\text{PhP}\text{β}\text{GP}$ ratio to the normal maximum. In the presence of T4 or HC, maltase activity rose in explanted strips at the same rate as in the intact duodenum, but it lagged in unsupplemented medium. Assay of the medium revealed, however, that under all conditions of culture a large amount of both maltase and ALP activity had been released from the tissue. This effect was especially pronounced in the presence of T4, so that explants and medium together accumulated ALP and maltase equivalent to the high peaks of activity found in the intact duodenum at hatching. With 10^?8M T4, ALP activity began to rise above that of control explants after 8 hr, with accumulation in the medium beginning about 4 hr later. Combining 2 × 10^?6M HC with a range of T4 concentrations produced greater than additive effects, particularly with ALP, but did not lead to enhanced retention of either enzyme in the tissue strips. Prolactin, pentagastrin, and insulin were without effect alone, but the latter inhibited the effects of both T4 and HC.