In vitro transcription and processing of a yeast tRNA gene containing an intervening sequence

A gene for Saccharomyces cerevisiae tRNATrp has been sequenced which contains an intervening sequence of 34 bp (H. S. Kang and J. Abelson, unpublished results). The mutant yeast strain ts-136 accumulates a precursor to tRNATrp which contains mature ends and is colinear with the tRNATrp gene. A nuclear extract from Xenopus oocytes is capable of supporting transcription of the tRNATrp gene contained on plasmid pBR313. The products are precursor tRNAs which contain the intervening RNA sequence. The Xenopus extract accurately splices the precursor transcript to mature-sized tRNATrp.

Virus-associated nucleases: location and properties of deoxyribonucleases and ribonucleases in purified frog virus 3

At least three nuclease activities are associated with purified frog virus 3. These activities are endodeoxyribonuclease (pH 7.5, double-stranded [DS] and single-stranded [SS] deoxyribonucleic acid [DNA]); endodeoxyribonuclease (pH 5.0, DS and SS DNA); endoribonuclease (DS and SS ribonucleic acid [RNA], pH 7.5). These activities are not adsorbed to the surface of the virion but are within the viral capsid and require detergent disruption of virions to unmask enzyme activity. Only one activity, deoxyribonuclease (pH 5.0, SS and DS DNA) appears to be core-associated after detergent disruption of virions. The ribonuclease degrades poliovirus replicative-form RNA, reovirus native RNA, and poly(I) poly(C) to a product with a sedimentation coefficient of about 6S. Qbeta 6S DS RNA and 4S transfer RNA are not degraded. The ribonuclease appears to be a late function of the virus and is elicited in a soluble form as well as a virus-associated form.

Deoxyribonucleic acid replication in simian virus 40-infected cells. IV. Two different requirements for protein synthesis during simian virus 40 deoxyribonucleic acid replication

The replication of simian virus 40 (SV40) deoxyribonucleic acid (DNA) was inhibited by 99% 2 hr after the addition of cycloheximide to SV40-infected primary African green monkey kidney cells. The levels of 25S (replicating) and 21S (mature) SV40 DNA synthesized after cycloheximide treatment were always lower than those observed in an infected untreated control culture. This is consistent with a requirement for a protein(s) or for protein synthesis at the initiation step in SV40 DNA replication. The relative proportion of 25S DNA as compared with 21S viral DNA increased with increasing time after cycloheximide treatment. Removal of cycloheximide from inhibited cultures allowed the recovery of viral DNA synthesis to normal levels within 3 hr. During the recovery period, the ratio of 25S DNA to 21S DNA was 10 times higher than that observed after a 30-min pulse with (3)H-thymidine with an infected untreated control culture. The accumulation of 25S replicating SV40 DNA during cycloheximide inhibition or shortly after its removal is interpreted to mean that a protein(s) or protein synthesis is required to convert the 25S replicating DNA to 21S mature viral DNA. Further evidence of a requirement for protein synthesis in the 25S to 21S conversion was obtained by comparing the rate of this conversion in growing and resting cells. The conversion of 25S DNA to 21S DNA took place at a faster rate in infected growing cells than in infected confluent monolayer cultures. A temperature-sensitive SV40 coat protein mutation (large-plaque SV40) had no effect on the replication of SV40 DNA at the nonpermissive temperature.

Studies on the effects of steroids on DNA synthesis of human chromosomes in vitro

Tritiated thymidine and autoradiographic techniques were used to investigate the sequence and pattern of DNA replication of sex chromosomes in cultured human cells treated with progesterone and testosterone.The average frequencies of progesterone- and testosterone-induced chromatid aberration were 19 and 26% respectively, whereas that of spontaneous aberration was 2.5%. No chromosome aberrations were found in sex chromosomes of either sex. Aberrations were distributed throughout cells in both S and G2stages. The general production of aberrations increased with increases in the time between isotopic labeling and fixation. The mean duration of G2was over 3 hours in the control, over 4.5 hours in the progesterone-treated group and 4.75 hours in the testosterone group. Thus, G2time for human kidney cells treated with steroids was delayed about 1 to 2 hours.Striking asynchrony of DNA duplication in homologous X chromosomes in steroids-treated female cells was also observed at the end of the period. However, even in metaphases that incorporated thymidine-H3at 6 hours before fixation the hot-X was detectable. The Y chromosome in male cells showed a high percentage of labeling intensity with particularly heavy grains, differing from that of G group. Metaphases of female cells labelled at 6 hours before fixation in progesterone had an unlabeled, chromosome in the complement of moderately labeled cells. This unlabeled chromosome was also found in testosterone-treated cells prepared 10 hours after labeling and is presumed to be heteropycnotic X chromosome.