Regional assignment of the gene for human liver/bone/kidney alkaline phosphatase to chromosome 1p36.1-p34

We have used three different methods to map the human liver/bone/kidney alkaline phosphatase (ALPL) locus: (1) Southern blot analysis of DNA derived from a panel of human-rodent somatic cell hybrids; (2) in situ hybridization to human chromosomes; and (3) genetic linkage analysis. Our results indicate that the ALPL locus maps to human chromosome bands 1p36.1-p34 and is genetically linked to the Rh (maximum lod score of 15.66 at a recombination value of 0.10) and fucosidase A (maximum lod score of 8.24 at a recombination value of 0.02) loci. These results, combined with restriction fragment length polymorphisms identified by ALPL DNA probes, provide a useful marker for gene mapping studies involving the short arm of chromosome 1. In addition, our results help to elucidate further the structure and evolution of the human alkaline phosphatase multigene enzyme family.     

Isolation and Partial Characterization of Escherichia coli Mutants with Low Levels of Transfer Ribonucleic Acid Nucleotidyltransferase

To determine the function of the enzyme transfer ribonucleic acid (tRNA) nucleotidyltransferase in vivo, five mutants of Escherichia coli containing low levels of this enzyme were isolated. Since no selection procedure for such mutants existed, these strains were isolated by assay of large numbers of colonies from a heavily mutagenized stock. A procedure employing cells made permeable to tRNA and ATP was used to screen the large number of colonies required for the isolation. All the mutants contained less than 20% of the normal level of the AMP-incorporating activity of tRNA nucleotidyltransferase in extracts prepared by several methods, and the best mutant contained only about 2% of this activity. Three of the mutants also had equally low levels of the cytidine 5'-monophosphate-incorporating activity of the enzyme. Despite these low activities, the mutant strains displayed relatively normal growth characteristics at all temperatures examined. The enzyme in the mutant strains was not temperature sensitive, nor were any other abnormal biochemical properties detected. tRNA isolated from the mutant strains was missing significant amounts of its 3' terminal adenosine 5'-monophosphate residue, amounting to 10 to 15% in the best mutant. However, only small amounts of the terminal cytidine 5'-monophosphate residue were missing. The results indicate that tRNA nucleotidyltransferase is involved in some aspect of synthesis or repair of the 3' terminus of tRNA, and that the enzyme is present in large excess over its requirements for this function.     

Sequence specificity of 125I-labelled Hoechst 33258 in intact human cells

Using polyacrylamide/urea DNA sequencing gels, the DNA sequence selectivity of 125I-labelled Hoechst 33258 damage has been determined in intact human cells to the exact base-pair. This was accomplished using a novel procedure with human alpha RI-DNA as the target DNA sequence. In this procedure, after size fractionation, the alpha RI-DNA is selectively purified by hybridization to a single-stranded M13 clone containing an alpha RI-DNA insert. The sequence specificity of [125I]Hoechst 33258 was indistinguishable in intact cells from purified high molecular weight DNA; and this is surprising considering the more complex environment of DNA in the nucleus where DNA is bound to nucleosomes and other DNA binding proteins. The ligand preferentially binds to DNA sequences which have four or more consecutive A.T base-pairs. The extent of damage was measured with a densitometer and, relative to the damage hotspot at base-pair 94, the extent of damage was similar in both purified high molecular weight DNA and intact cells. [125I]Hoechst 33258 causes only double-strand breaks, since single-strand breaks or base damage were not detected. These experiments represent the first occasion that the sequence specificity of a DNA damaging agent, which causes only double-strand breaks, has been determined to the exact base-pair in intact cells.     

The detection and purification of a cat uterine secretory protein that is estrogen dependent (CUPED)

An estrogen-dependent secretory protein (CUPED) was detected and purified from uterine flushings of ovariectomized cats treated with 17 beta-estradiol. The protein was not detected in uterine flushings obtained from untreated ovariectomized animals or estrogen-primed animals treated with progesterone for 4 days. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of uterine flushings showed the presence of 1 or 2 protein bands with relative mobility values less than reduced and denatured thyroglobulin (Mr = 330,000). The protein was purified by differential centrifugation and gel filtration chromatography. Antiserum was raised against this purified protein in rabbits. The specificity of the antiserum to uterine fluid proteins was assessed by immunoblotting of electrophoretically transferred proteins. The antiserum cross-reacted with electrophoretically separated CUPED protein bands in uterine flushings. This protein may represent the content of the estradiol-induced secretory granules present in endometrial epithelial cells.     

A non-enzymic procedure for the quantitative analysis of (3-methoxy-4-sulphoxyphenyl)ethylene glycol (MHPG sulphate) in human urine using stable isotope dilution and gas chromatography—mass spectrometry

A method is described for the quantitative analysis of (3-methoxy-4-sulphoxyphenyl)-ethylene glycol (MHPG sulphate) in human urine, based on selected ion monitoring gas chromatography—mass spectrometry and using a specifically deuterium-labelled analogue of MHPG sulphate as internal standard. The procedure involves extraction of the urine sample on Amberlite XAD-2, followed by isolation of MHPG sulphate by column chromatography on Sephadex LH-20. Cleavage of the sulphate conjugate and formation of the MHPG tris(trifluoroscetate) derivative are carried out in a one-step reaction, without recourse to enzymic hydrolysis.     

Catalytic Properties of RNase BN/RNase Z from Escherichia coli: RNase BN IS BOTH AN EXO- AND ENDORIBONUCLEASE*

Processing of the 3′ terminus of tRNA in many organisms is carried out by an endoribonuclease termed RNase Z or 3′-tRNase, which cleaves after the discriminator nucleotide to allow addition of the universal -CCA sequence. In some eubacteria, such as Escherichia coli, the -CCA sequence is encoded in all known tRNA genes. Nevertheless, an RNase Z homologue (RNase BN) is still present, even though its action is not needed for tRNA maturation. To help identify which RNA molecules might be potential substrates for RNase BN, we carried out a detailed examination of its specificity and catalytic potential using a variety of synthetic substrates. We show here that RNase BN is active on both double- and single-stranded RNA but that duplex RNA is preferred. The enzyme displays a profound base specificity, showing no activity on runs of C residues. RNase BN is strongly inhibited by the presence of a 3′-CCA sequence or a 3′-phosphoryl group. Digestion by RNase BN leads to 3-mers as the limit products, but the rate slows on molecules shorter than 10 nucleotides in length. Most interestingly, RNase BN acts as a distributive exoribonuclease on some substrates, releasing mononucleotides and a ladder of digestion products. However, RNase BN also cleaves endonucleolytically, releasing 3′ fragments as short as 4 nucleotides. Although the presence of a 3′-phosphoryl group abolishes exoribonuclease action, it has no effect on the endoribonucleolytic cleavages. These data suggest that RNase BN may differ from other members of the RNase Z family, and they provide important information to be considered in identifying a physiological role for this enzyme.Maturation of tRNA precursors requires the removal of 5′ and 3′ precursor-specific sequences to generate the mature, functional tRNA (1). In eukaryotes, archaea, and certain eubacteria, the 3′-processing step is carried out by an endoribonuclease termed RNase Z or 3′-tRNase (2–6). However, in some bacteria, such as Escherichia coli, removal of 3′ extra residues is catalyzed by any of a number of exoribonucleases (7, 8). The major determinant for which mode of 3′-processing is utilized appears to be whether or not the universal 3′-terminal CCA sequence is encoded (2, 9). Thus, for those tRNA precursors in which the CCA sequence is absent, endonucleolytic cleavage by RNase Z right after the discriminator nucleotide generates a substrate for subsequent CCA addition by tRNA nucleotidyltransferase (1–3, 10). In view of this role for RNase Z in 3′-tRNA maturation, it is surprising that E. coli, an organism in which the CCA sequence is encoded in all tRNA genes (2), nevertheless contains an RNase Z homologue (11), because its action would appear not to be necessary. In fact, the physiological function of this enzyme in E. coli remains unclear, because mutants lacking this protein have no obvious growth phenotype (12). Hence, there is considerable interest in understanding the enzymatic capabilities of this enzyme.The E. coli RNase Z homologue initially was identified as a zinc phosphodiesterase (11) encoded by the elaC gene (now called rbn) (13). Subsequent work showed that the protein also displayed endoribonuclease activity on certain tRNA precursors in vitro (6, 14). However, more recent studies revealed that this protein actually is RNase BN, an enzyme originally discovered in 1983 and shown to be essential for maturation of those bacteriophage T4 tRNA precursors that lack a CCA sequence (15, 16). Using synthetic mimics of these T4 tRNA precursors, RNase BN was found to remove their 3′-terminal residue as a mononucleotide to generate a substrate for tRNA nucleotidyltransferase. Based on these reactions RNase BN was originally thought to be an exoribonuclease (13, 15, 17). However, subsequent work by us and others showed that it can act as an endoribonuclease on tRNA precursors (13, 18). RNase BN is required for maturation of tRNA precursors in E. coli mutant strains devoid of all other 3′-tRNA maturation exoribonucleases, although it is the least efficient RNase in this regard (7, 19). Thus, under normal circumstances, it is unlikely that RNase BN functions in maturation of tRNA in vivo except in phage T4-infected cells (15, 16).To obtain additional information on what types of RNA molecules might be substrates for RNase BN and to clarify whether it is an exo- or endoribonuclease, we have carried out a detailed examination of its catalytic properties and substrate specificity. We show here that RNase BN has both exo- and endoribonuclease activity and that it can act on a wide variety of RNA substrates. These findings suggest that E. coli RNase BN may differ from other members of the RNase Z family of enzymes.