Considerable portions of cells in cultured carrot root disks replicate DNA in a synchronous fashion, with a maximum peak of synthesis at 48h after excision of the disks. At the early stage of this first replication phase, a satellite DNA component with a higher buoyant density is preferentially synthesized. DNA from the root explants, pulse-labeled with 3H-thymidine at the early (15h) and middle (48h) synthetic stages, sedimented in the 5-9S region in an alkaline sucrose density gradient. After prolonged labeling or chase incubation, the 3H-radioactivity shifted from the 5-9S components to longer intermediate molecules of 10-11S, 12-13S, 18-20S, and 24-26S with the bulk DNA synthesized at the middle stage, but this shift appeared to be delayed with the satellite DNA synthesized at the early stage. The results of chromatographic fractionation of EcoRI-digests of 2h-labeled DNA, and the EcoRI-digests treated additionally with S1-nuclease over benzoylated naphthoylated DEAE-cellulose, indicated that the relative ratio of DNA molecules containing substantial single-stranded regions to predominantly double-stranded molecules was clearly higher in the early replicating DNA.
Protoplasts isolated from suspension cultured cells of orange (Citrus sinensis Osb.) were treated with a bacterial plasmid DNA carrying a chimeric gene consisting of the nopaline synthase promoter, the aminoglycoside phosphotransferase II [APH(3′)II] structural gene from the bacterial transposon Tn 5 and a terminator region from cauliflower mosaic virus DNA. Colonies capable of proliferating in a medium containing kanamycin (25μg/ml) possessed APH(3′)II activity and an intact foreign gene. The transformation frequency was recorded to be in the order of 10-6.
A reciprocal cross difference in the frequency of male recombination was detected in progeny of hybrids between e se; bri ru and Tonga stocks of Drosophila ananassae. A chromosomal enhancer-cytoplasmic suppressor system determining male crossing over in D. ananassae was identified that appeared to be similar to, but distinct from, that described previously by Hinton (1974). The higher the temperature at which males were reared, the less reciprocal cross ratio in the frequency of male recombination was found. The reciprocal cross differences might be explained by a cytoplasmic suppressor of the Tonga stock and a nuclear chromosomal gene(s). This chromosomal gene is dominant for the reducing the frequency of male recombination, and is located on the 2nd chromosome of the Tonga stock. The maternally transmitted cytoplasmic suppressor was maintained by other chromosomal regions (genes) on both 2nd and 3rd chromosomes of the Tonga stock.
The wild type div-341+ gene of Bacillus subtilis was cloned in a temperate phage ρ11, and was recloned in a smaller temperate phage φ105. The resulting Div+ transducing phage carried a 3 kilobase Cfr13I digested chromosomal fragment which showed Div+ transforming activity and contained the whole div-341+ gene which is involved in cell division, sporulation, exoenzyme secretion, competent cell formation, and autolysis. A partial restriction map of the fragment was established. The merodiploid system of the div-341+ gene, wild type gene on the phage genome and mutant gene on the chromosome, resulted in the suppression of mutant phenotypes and indicated that the wild type div-341+ gene is dominant over mutant gene.
An attempt was made in the present study to express mouse tyrosinase cDNAs fused with the authentic genomic 5′ non-coding flanking sequence in cultured albino melanocytes. One of the cDNA sequences, which expressed successfully and produced melanin pigments, was analyzed with respect to deduced amino acid sequence. Sequencing of the tyrosinase genomic gene revealed the existence of several sets of a characteristic structure which consists of a chain of two successive stem structures, CCAAT-homology and TATA box at its 5′ non-coding region. It seems possible that this region represents the regulatory element of the tyrosinase gene. Unusually long GA cluster at 5′ upstream region was also found.