Replication variants of the human inactive X chromosome

The sequence of DNA replication was studied within the inactive X chromosome in human lymphocytes, by means of the FPG method. Several variants of the replication sequence were found. The number of variants in the cells of a single donor exceeded 2 in each of the 4 normal individuals studied. The phenomenon is discussed with respect to the regulation of DNA synthesis and to the cell differentiation process.     

Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome). An intermediate clinical phenotype caused by substitution of valine for glycine at position 137 of arylsulfatase B.

The Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI) is a lysosomal storage disease with autosomal recessive inheritance caused by deficiency of the enzyme arylsulfatase B. Severe, intermediate, and mild forms of the disease have been described. The molecular correlate of the clinical heterogeneity is not known at present. To identify the molecular defect in a patient with the intermediate form of the disease, arylsulfatase B mRNA from his fibroblasts was reverse-transcribed, amplified by the polymerase chain reaction, and subcloned. Three point mutations were detected by DNA sequence analysis, two of which, a silent A to G transition at nucleotide 1191 and a G to A transition at nucleotide 1126 resulting in a methionine for valine 376 substitution, were polymorphisms. A G to T transversion at nucleotide 410 causing a valine for glycine 137 substitution (G137V) was identified as the mutation underlying the Maroteaux-Lamy phenotype of the patient, who was homozygous for the allele. The kinetic parameters of the mutant arylsulfatase B enzyme toward a radiolabeled trisaccharide substrate were normal excluding an alteration of the active site. The G137V mutation did not affect the synthesis but severely reduced the stability of the arylsulfatase B precursor. While the wild type precursor is converted by limited proteolysis in late endosomes or lysosomes to a mature form, the majority of the mutant precursor was degraded presumably in a compartment proximal to the trans Golgi network and only a small amount escaped to the lysosomes accounting for the low residual enzyme activity in fibroblasts of a patient with the juvenile form of the disease.     

On the evolution of the bacterial major sigma factors

Summary The existence of internal sequence homologies between the N-terminal halves of the gram-negative bacterial major sigma factors and their C-terminal halves, which correspond to minor factors, is reported. In the case of Escherichia-Salmonella sigma-70, an apparent homology was even found between the C-terminal helix-turn-helix DNA-binding motif and the corresponding region of the peptide N half, which, however, is not directly engaged in promoter recognition. It is proposed that major sigma factors may have originated by duplication and fusion of a DNA unit related to the ancestral gene for the whole sigma family. Coevolution of major sigma structures and complex promoters is suggested.     

Insulin-like growth factor II overexpression does not affect sorting of lysosomal enzymes in NIH-3T3 cells.

The sorting of newly synthesized mannose 6-phosphate (M6P)-containing proteins and of the major excreted protein (MEP), a lysosomal thiol proteinase, was studied in NIH-3T3 cells transfected with the cDNA of human insulin-like growth factor II (IGF II) or with the vector alone. Extracts from media and cells labelled with [35S] methionine were used for chromatography on a M6P/IGF II receptor affinity matrix or for immunoprecipitation to assess the distribution of newly synthesized M6P-containing proteins and MEP, respectively. The results indicate that the overexpression of IGF II did not affect the synthesis and the sorting of M6P-containing proteins and of MEP. The binding and uptake of the lysosomal enzyme arylsulfatase A were not affected in IGF II overexpressing cells.     

Genetic polymorphism of erythrocyte histone H1 in Japanese quail

Histone H1 from erythrocytes of Japanese quail was resolved in a sodium dodecyl sulfate (SDS)-polyacrylamide gel into five fractions differing in apparent molecular weights. A polymorphism of histone H1.1, H1.2, and H1.3 bands was detected among quail individuals. While some birds possessed either a high (phenotype .3+) or a low (phenotype .3+/.3-) level of H1.3, at least half of the quail population lacked this H1 band (phenotype .3-). Appropriate genetic crosses demonstrated that H1.3 behaved as though it was coded by a gene with two codominant alleles at an autosomal locus. Using two-dimensional polyacrylamide gel electrophoresis (acid-urea followed by SDS gels), it was found that birds .3+ contained polypeptides H1.b1 and H1.b'1; birds .3-, polypeptides H1.b2 and H1.b'2 with lower apparent molecular weights; and birds .3+/.3-, both types of polypeptides in equal proportions. The H1.b2 + H1.b'2 complement was not discernible in SDS gels, for it migrated together with H1.c' within band H1.4. It was found that a small number of birds lacking the H1.2 band in SDS gels failed to express histone H1.a. Since birds with phenotype .2- with a defective allele of the gene H1.a were simultaneously lacking the H1.3 band, it seems that the imperfect allele of the H1.a gene might be closely linked to the alleles producing H1.b2 + H1.b'2.     

Quaternary structure of the Mr 46,000 mannose 6-phosphate specific receptor: effect of ligand, pH, and receptor concentration on the equilibrium between dimeric and tetrameric receptor forms

The Mr 46,000 mannose 6-phosphate specific receptor exists in solution as a mixture of noncovalently associated dimeric and tetrameric forms. The two quaternary forms were separated by sucrose density centrifugation, and their composition was assessed by cross-linking with bifunctional reagents followed by SDS-polyacrylamide gel electrophoresis. The dependence of equilibrium between the dimeric and tetrameric forms on pH, receptor concentration, and presence of mannose 6-phosphate was studied. The formation of tetrameric forms is favored by pH values around 7, high receptor concentration, and presence of mannose 6-phosphate ligand. Tetrameric forms bind stronger at pH 7 to phosphomannan-Sepharose 4B than dimeric forms. Both quaternary forms dissociate at the same pH from a mannose 6-phosphate affinity matrix. When starting with dimeric or tetrameric forms, the equilibrium between dimeric and tetrameric forms is reached at pH 7.5 and 4 degrees C after 6-8 days. The presence of 5 mM mannose 6-phosphate shifts the equilibrium toward tetrameric forms. At pH 4.5 and 4 degrees C, the association of dimeric to tetrameric forms is negligible, while tetrameric forms dissociate to dimeric forms within 12 h. The results demonstrate that oligomerization is an intrinsic property of MPR-46 that is affected by ligand binding, pH, and receptor concentration.     

Tetracyclic triterpenes. Part VI [1] . The synthesis of 4,4,14α-Trimethyl-19 ( 10 → 9β) abeo-steroids. Synthons for the preparation of cucurbitacins

The effective synthesis of 4,4,14α-trimethyl-19 (10 → 9β) abeo-steroids (iv), (v), and (Vl) with two- and five-carbon side chains from lanosterol is described. Their structures were proved on the basis of spectral data. The title compounds are the first synthetic synthons for the preparation of 4,4,14α-trimethyl-steroids with an unnatural configuration.     

Processing of the phosphorylated recognition marker in lysosomal enzymes. Characterization and partial purification of a microsomal alpha-N-acetylglucosaminyl phosphodiesterase

N-Acetylglucosamine(1)phospho(6)mannose groups recently identified in lysosomal enzymes were proposed to be precursors of the recognition markers terminating with mannose 6-phosphate (Tabas, I., and Kornfeld, S. (1980) J. Biol. Chem. 225, 6633-6639; Hasilik, A., Klein, U., Waheed, A., Strecker, G., and von Figura, K. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 7074-7078). To study the presumptive enzyme removing N-acetylglucosamine from the diester, an assay was developed using a radioactive oligosaccharide containing diester groups of the above structure. An alpha-N-acetylglucosaminyl phosphodiesterase cleaving this substrate in vitro was found in human placenta and in rat liver. The enzyme was solubilized from the microsomal fraction of human placenta and more than 800-fold purified with 75% yield. It is distinct from the lysosomal alpha-N-acetylglucosaminidase by the criteria of immunological cross-reactivity, substrate specificity, and heat stability. The partially purified enzyme cleaves alpha-N-acetylglucosamine phosphodiester bonds in oligosaccharides from lysosomal enzymes, in lysosomal enzymes, and in UDP-N-acetylglucosamine. We propose that the microsomal alpha-N-acetylglucosaminyl phosphodiesterase is involved in the processing of the phosphorylated recognition marker in lysosomal enzymes.