Collagen defects in lethal perinatal osteogenesis imperfecta.

Quantitative and qualitative abnormalities of collagen were observed in tissues and fibroblast cultures from 17 consecutive cases of lethal perinatal osteogenesis imperfecta (OI). The content of type I collagen was reduced in OI dermis and bone and the content of type III collagen was also reduced in the dermis. Normal bone contained 99.3% type I and 0.7% type V collagen whereas OI bone contained a lower proportion of type I, a greater proportion of type V and a significant amount of type III collagen. The type III and V collagens appeared to be structurally normal. In contrast, abnormal type I collagen chains, which migrated slowly on electrophoresis, were observed in all babies with OI. Cultured fibroblasts from five babies produced a mixture of normal and abnormal type I collagens; the abnormal collagen was not secreted in two cases and was slowly secreted in the others. Fibroblasts from 12 babies produced only abnormal type I collagens and they were also secreted slowly. The slower electrophoretic migration of the abnormal chains was due to enzymic overmodification of the lysine residues. The distribution of the cyanogen bromide peptides containing the overmodified residues was used to localize the underlying structural abnormalities to three regions of the type I procollagen chains. These regions included the carboxy-propeptide of the pro alpha 1(I)-chain, the helical alpha 1(I) CB7 peptide and the helical alpha 1(I) CB8 and CB3 peptides. In one baby a basic charge mutation was observed in the alpha 1(I) CB7 peptide and in another baby a basic charge mutation was observed in the alpha 1(I) CB8 peptide. The primary defects in lethal perinatal OI appear to reside in the type I collagen chains. Type III and V collagens did not appear to compensate for the deficiency of type I collagen in the tissues.     

Molecular characterization of the gene coding for major outer membrane protein OmpA from Enterobacter aerogenes

The ompA gene from Enterobacter aerogenes was subcloned into a low-copy-number plasmid vector and the resultant plasmid, pTU7En, used to study its expression in Escherichia coli K12. Although the gene was strongly expressed and large amounts of OmpA protein were present in the outer membrane its product was not functionally identical to the E. coli polypeptide. In particular, the E. aerogenes OmpA protein was unable to confer sensitivity to OmpA-specific phages of E. coli. When the primary structure of the protein was deduced from the nucleotide sequence of its gene it was found that three domains differed extensively from the corresponding regions of the E. coli protein. As two of these are known to be exposed on the cell surface we inferred that these alterations are responsible for differences in the biological activity of the two proteins.     

A comparison of the agar cloning and microtitration techniques for assaying cell survival and mutation frequency in L5178Y mouse lymphoma cells

Microtitration methods for assaying cell survival and mutation frequency to ouabain resistance, 6-thioguanine resistance and 1-β-d-arabinofuranosyl cytosine resistance in L5178Y mouse lymphoma cells were compared to the standard agar cloning technique. The two methods gave essentially similar results for untreated cells, and after treatment with ethyl methanesulphonate and 4-nitroquinoline 1-oxide. Potential advantages of the microtitration method as a routine assay system are discussed.     

Differential reactivity of human low density lipoproteins with monoclonal antibodies

The immunoreactivities of LDL (low density lipoprotein) samples obtained from a variety of subjects were analyzed by comparing their capacities to compete with 125I-labeled LDL for binding to various monoclonal anti-LDL antibodies in competitive binding assays. A marked variation in epitope expression was observed. In comparison to an LDL standard, different preparations exhibited immunoreactivities (expressed as apparent apoB content) ranging from 30 to 400% of the LDL standard. Some epitopes were much more uniformly expressed than others. The number of epitopes expressed in different LDL preparations appeared to be related to the percentage composition of various lipid constituents in LDL. The results support the hypothesis that the epitope expression of apoB is modulated by the composition of the lipids associated with it.     

Melting order of successively longer yeast phenylalanine-accepting transfer ribonucleic acid fragments with a common 5' end

Temperature-jump methods were used to study the kinetics of the helix to coil transition in three fragments of yeast tRNAPhe that share a common 5' terminus (the 5' end of the mature tRNA). Correlation of the extrapolated helix dissociation time constants with NMR exchange broadening results allows assignment of the structural basis of the optical melting transition in the fragments. The results confirm nuclear magnetic resonance findings on these fragments: the 5' 1/4 fragment has no helical structure; the 5' 1/2 fragment contains the D stem; and the 5' 3/5 fragment contains the D stem and the anticodon stem. These are the structures expected if sequential folding of the tRNA during biosynthesis were to occur. The D stem is the last helix to melt in the 5' 3/5 fragment. We suggest that structural elements in addition to the four Watson-Crick base pairs of the D-stem helix are responsible for the anomalously high Tm of that hairpin.     

FOETAL ERYTHROPOIESIS IN GENETICALLY ANAEMIC, FLEXED-TAILED (f/f) MICE

This paper presents measurements of foetal weights, haemoglobin concentrations, red cell counts, blood volumes, erythroblast thymidine labelling indices and cell cycle parameters in genetically anaemic, flexed-tailed ( f/f ) and haematologically normal ( f/+ ) foetuses.
The production of red blood cells from the livers of ( f/f ) foetal mice lags behind that of heterozygote ( f/+ ) foetuses, and the cells that are produced are small and poorly haemoglobinized. The anaemia is not due to an abnormal cell cycle in f/f erythroblasts, which appear to be capable of responding to the anaemia by a small increase in their rates of proliferation. The number of red cells in the foetal circulation can be calculated from the cell cycle time and number of hepatic erythroblasts; the calculated number agrees quite well with the measured number in both f/f and f/+ foetuses. Many characteristics of the anaemia of the f/f foetus can be accounted for if it is assumed that there is a deficiency in the production or activity of an enzyme involved early in the haem synthetic pathway.