Regulation of DNA replication by homopurine/homopyrimidine sequences

The simple repeating homopurine/homopyrimidine sequences dispersed throughout many eukaryotic genomes are known to form triple helical structures comprising three-stranded and single-stranded DNA. Several lines of evidence suggest that these structures influence DNA replication in cells. Homopurine/homopyrimidine sequences cloned into simian virus 40 (SV40) or SV40 origin-containing plasmids caused a reduced rate of DNA synthesis due to the pausing of replication forks. More prominent arrests were observed in in vitro experiments using single-stranded and double-stranded DNA with triplex-forming sequences. Nucleotides unable to form triplexes when present in the template DNA or when incorporated into the nascent strand prevented termination. Similarly, mutations destroying the triplex potential did not cause arrest while compensatory mutations restoring triplex potential restored it. These and other observations from a number of laboratories indicating that homopurine/homopyrimidine sequences act as arrest signals in vitro and as pause sites in vivo during replication fork movement suggest that these naturally occurring sequences play a regulatory role in DNA replication and gene amplification.     

Ethanol-dependent oxygen consumption and acetaldehyde formation during vanadyl oxidation by H2O2

Sequential addition of vanadyl sulfate to a phosphate-buffered solution of H₂O₂ released oxygen only after the second batch of vanadyl. Ethanol added to such reaction mixtures progressively decreased oxygen release and increased oxygen consumption during oxidation of vanadyl by H₂O₂. Inclusion of ethanol after any of the three batches of vanadyl resulted in varying amounts of oxygen consumption, a property also shared by other alcohols (methanol, propanol and octanol). On increasing the concentration of ethanol, vanadyl sulfate or H₂O₂, both oxygen consumption and acetaldehyde formation increased progressively. Formation of acetaldehyde decreased with increase in the ratio of vanadyl:H₂O₂ above 2:1 and was undetectable with ethanol at 0.1 mM. The reaction mixture which was acidic in the absence of phosphate buffer (pH 7.0), released oxygen immediately after the first addition of vanadyl and also in presence of ethanol soon after initial rapid consumption of oxygen, with no accompanying acetaldehyde formation. The results underscore the importance of some vanadium complexes formed during vanadyl oxidation in the accompanying oxygen-transfer reactions.     

Differential cleavage and developmental rates and their correlation with cell numbers and sex ratios in buffalo embryos generated in vitro

In vitro matured and fertilized buffalo oocytes were co-cultured with buffalo oviductal epithelial cells (BOEC) in CRlaa medium. Cleaved embryos were separated according to the time of completion of first cleavage (i.e., before 30 h and after 30 h post insemination) and cultured for 5 to 10 d and allowed to develop to the blastocyst stage. Zygotes cleaving before 30 h were termed fast-cleaving while those cleaving after 30 h were termed slow-cleaving. The results indicated that fast-cleaving embryos are more likely to develop into blastocysts (25%) than slow-cleaving embryos (7.8%). The quality and viability of fast-cleaving and fast-developing blastocysts was found to be better than that of slow-cleaving, slow-developing blastocysts as judged by cell numbers (67.7 +/- 3.7 vs 35.2 +/- 2.1). However, the mitotic index was not different between the 2 groups. The sex of fast-developing and slow-developing blastocysts was determined via the polymerase chain reaction (PCR) to correlate the rate of embryonic development with the sex ratio of the embryos. Embryos produced by Bull 293 and Bull M-82, irrespective of their being fast or slow-developing, gave rise to more females and males, respectively. From these results, we suggest that there may be a sire effect on sex ratio of in vitro produced buffalo embryos.     

Production of hybrids, amphiploids and backcross progenies between a cold-tolerant wild species, Erucastrum abyssinicum and crop brassicas

Three intergeneric hybrids were produced between a cold-tolerant wild species, Erucastrum abyssinicum and three cultivated species of Brassica, B. juncea, B. carinata and B. oleracea, through ovary culture. The hybrids were characterized by morphology, cytology and DNA analysis. Amphiploidy was induced in all the F₁ hybrids through colchicine treatment. Stable amphiploids and backcross progenies were obtained from two of the crosses, E. abyssinicum x B. juncea and E. abyssinicum x B. carinata. The amphiploid, E. abyssinicum x B. juncea was successfully used as a bridge species to produce hybrids with B. napus, B. campestris and B. nigra. These hybrids and backcross progenies provide useful genetic variability for the improvement of crop brassicas.     

Regulated nuclear polyadenylation of Xenopus albumin pre-mRNA.

Cytoplasmic regulation of the length of poly(A) on mRNA is a well-characterized process involved in translational control during development. In contrast, there is no direct in vivo evidence for regulation of the length of poly(A) added during nuclear pre-mRNA processing in somatic cells. We previously reported that Xenopus serum albumin [Schoenberg et al. (1989) Mol. Endocrinol. 3, 805-815] and transferrin [Pastori et al. (1992) J. Steroid Biochem. Mol. Biol. 42, 649-657], mRNA have exceptionally short poly(A) tails ranging from 12 to 17 residues, whereas vitellogenin mRNA has long poly(A). An RT-PCR protocol was adapted to determine the length of poly(A) added onto pre-mRNA, defined here as that species bearing the terminal intron. Using this assay we show that vitellogenin pre-mRNA has the same long poly(A) tail as mature vitellogenin mRNA. In contrast, albumin pre-mRNA has the same short poly(A) as found on fully-processed albumin mRNA. These results indicate that the short poly(A) tail on albumin mRNA results from regulation of poly(A) addition during nuclear 3' processing.     

Identification and sequence characterization of a 1.3 Kb EcoRI repeat fragment that harbors a DNA repair site of rat pachytene spermatocytes

Introduction of well-programmed nicks and gaps and the associated DNA repair activity in the genome at the pachytene interval is a characteristic feature of the meiotic prophase in organisms as varied as lilium and mouse. In the present study we have shown that the DNA synthetic activity in rat pachytene spermatocytes is insensitive to aphidicolin, a specific inhibitor of DNA polymerase , and , suggesting DNA -polymerase-mediated repair synthesis in these cells. We have developed a novel approach for the isolation of the DNA repair sites by combining two independent techniques. Following incorporation of BrdUrd into pachytene spermatocytes in the presence of aphidicolin, the repair sites were released as ssDNA fragments by treatment of nuclei with 30 mM NaOH. Subsequently, the BrdUrd containing ssDNA fragments were specifically isolated using polyclonal anti-BrdUrd antibodies. The DNA fragments released were of two size classes, namely 4–7S (major) and 9–12S (minor) and constituted approximately 1.75% of the pachytene genomic DNA. These DNA repair fragments were distinct from Okazaki fragments and other replicative intermediates isolated from rat bone marrow cells as evidenced by (a) their different size distribution and (b) little cross-hybridization. Southern hybridization of restriction enzyme digests of rat genomic DNA with probes made against BrdUrd-ssDNA fragments revealed that although the repair sites were distributed throughout the genome, strong hybridization signals were observed in EcoRI, (1.3 kb and 2.4 kb), BamH1 (9 kb) and HindIII (5 kb) repetetive DNA fragments. The EcoRI 1.3 kb family were cloned into M13 mp19, and a repair positive (1.3 A) and a repair negative (1.3 B) were identified and sequenced. The repair positive clone contained (a) (CA)₂₂ repeat, (b) a (CAGA)₆ repeat and (c) 4 sequences sharing high homology with various hypervariable minisatellite (HVMS) sequences. One of the HVMS sequence contained a GGCAGG motif known to be responsible for germline instability. The repair negative clone had (a) (CA)₆ repeat and (b) a HVMS like sequence without GGCAGG. The significance of these motifs and their relevance to the events of DNA metabolism at pachytene interval have been discussed.     

Chirospecific synthesis of D and Lp-chlorohomophenylalanine N-t-BOC DCHA salts

Summary The chirospecific conversions of D-glucosamine hydrochloride and D-mannosamine hydrochloride to the configurationally stable L and D isomers of N-t-butyloxycarbonylserinal were carried out byt-butylcarbonylation followed by sodium borohydride reduction and sodium meta-periodate oxidation. Reaction of the L and D aldehydes with the Wittig reagent prepared from 4-chlorobenzyltriphenylphosphonium chloride and butyl lithium followed by catalytic hydrogenation, Jones oxidation and salt formation with dicyclohexylamine gave the DCHA salts of the D and L isomers ofp-chlorohomophenylalanine N-t-Boc in high enatiomeric excess. The optical purity of the title compounds was established by hydrolysis to the respective free amino acids, followed by chiral derivatization and HPLC analysis.This was presented at the Fifth International Kyoto Conference on new Aspects of Organic Chemistry, Kyoto, Japan, November 11–15, 1991. Abstract #GO-13.     

Molecular cytogenetic analysis of a duplication Xp in a male: further delineation of a possible sex influencing region on the X chromosome

We describe a male infant with severe mental retardation and autism with a duplication of the short arm of the X chromosome. Chromosome painting confirmed the origin of this X duplication. Molecular cytogenetic analysis with fluorescence in situ hybridization (FISH) identified one copy of the zinc finger protein on the X chromosome (ZFX) and two copies of the steroid sulfatase gene (STS), further delineating the breakpoints. Based on cytogenetic and molecular comparisons of cases from the literature of sex-reversal in dup(X),Y patients and our patient, we suggest that a possible secondary sexinfluencing gene involved in the regulation of sex determination or testis morphogenesis is present at the distal Xp21.1 to p21.2 region.     

Topology of wolfgram proteins and 2′, 3′-cyclic nucleotide 3′-phosphodiesterase in CNS myelin: Studies with proteases

The topological disposition of Wolfgram proteins (WP) and their relationship with 2, 3-cyclic nucleotide 3-phosphodiesterase (CNPase) in human, rat, sheep, bovine, guinea pig and chicken CNS myelin was investigated. Controlled digestion of myelin with trypsin gave a 35KDa protein band (WP-t) when electrophoresed on dodecyl sulfate-polyacrylamide gel in all species. Western blot analysis showed that the WP-t was derived from WP. WP-t was also formed when rat myelin was treated with other proteases such as kallikrein, thermolysin and leucine aminopeptidase. Staining for CNPase activity on nitrocellulose blots showed that WP-t is enzymatically active. Much of the CNPase activity remained with the membrane fraction even after treatment with high concentrations of trypsin when WP were completely hydrolysed and no protein bands with M.W>14KDa were detected on the gels. Therefore protein fragments of WP with M.W<14KDa may contain CNPase activity. From these results, it is suggested that the topological disposition of all the various WP is such that a 35KDa fragment is embedded in the lipid bilayer and the remaining fragment exposed at the intraperiod line in the myelin structure which may play a role in the initiation of myelinogenesis.     

Neisseria gonorrhoeae possesses two nicotinamide adenine dinucleotide-independent lactate dehydrogenases

Abstract An important metabolic capability of Neisseria gonorrhoeae is the utilization of host-derived lactate. Two isoenzymes of the membrane-associated, pyridine dinucleotide-independent type of lactate dehydrogenase (iLDH) participate in lactate assimilation, but exhibit distinctive properties. Isoenzyme iLDH-I utilized lactate exclusively as substrate, exhibiting a preference for the D-isomer. In contrast, isoenzyme iLDH-II exhibited broad substrate specificity (lactate, phenyllactate, and 4-hydroxyphenyllactate), but was stereospecific for the L-isomers. These results explain the difficulty in isolating mutants unable to utilize lactate.