An aphid-transmissible (AT) and two non-aphid-transmissible (NAT) isolates of zucchini yellow mosaic virus (ZYMV) were studied. The predicted amino acid sequences of the coat protein (CP) of the three virus isolates were analysed and compared. The NAT isolates differed from the AT isolate in having a Thr instead of an Ala residue at position 10 in the conserved Asp-Ala-Gly triplet in the N-terminal region of CP. Aphid transmissibility was restored in a progeny virus derived from an infectious clone of the ZYMV-NAT isolate in which Thr was changed back to Ala by site-directed mutagenesis. However this mutation did not have any effect on the multiplication rate in squash, which was significantly higher than that of the AT isolate. The involvement of this mutation in aphid transmission and virus multiplication is discussed.
The effect of ribonucleosides and deoxyribonucleosides on the phosphorolysis of 5-fluoro-2′-deoxyuridine (FUdR) was examined in cells of Escherichia coli . All nucleosides tested except guanosine and deoxyguanosine inhibited phosphorolysis. By using genetically marked strains it was found that in vivo FUdR is a specific substrate of thymidine phosphorylase.
A plasmid containing promoter-deleted inactive beta-galactosidase gene [1] was used to select promoters of the pEP 121 plasmid [2]. Colonies of cells harboring reactivated beta-galactosidase gene were identified by their red color on McConkey plates. The quantitative amounts of beta-galactosidase produced in each clone were estimated by assaying enzyme activity and by measuring the specific beta-galactosidase protein following fractionation of total cells' proteins on polyacrylamide gel. A wide range of enzyme activities was observed. The most active promoter isolated was shown to promote beta-galactosidase production more efficiently, compared with the original beta-galactosidase promoter, amounting to 20% of all cell proteins. Such highly active promoters may be utilized in the future, to promote expression of cloned genes in bacteria.
RNA from chloroplasts isolated from Spirodela oligorrhiza included relatively rapidly-labeled fractions with apparent molecular weights of 2.7; 1.2; 0.7; and 0.5×106. With longer labeling, radioactivity appeared in the mature rRNAs (1.1 and 0.56×106 MW). Chloramphenicol inhibited the appearance of labeled mature rRNA, but increased the net labeling and caused the accumulation of the pulse-labeled RNAs, effects similar to those reported for bacteria.
