An unusually long repeated DNA sequence was identified in cloned DNA, three kb 3' to the human beta-globin gene. Other members of this repeated sequence family were isolated from a human genomic DNA library and characterized by Southern blotting techniques, electron microscopy, and solution hybridization. The copy located next to the beta-globin gene was found to be 6.4 +/- 0.2 kb long and continuous over that length. This repeated sequence family comprises about 1% of the human genome and contains 3000-4800 copies of moderate sequence divergence which are interspersed with other less-highly repeated DNA. The 6.4 kb repeated unit does not appear to be composed of any smaller tandemly repeated subunits, nor is it expressed at a high level in bone marrow cell RNA.

Epidemiological and immunological evidence indicates that the K1 capsular polysaccharide confers the property of virulence on Escherichia coli. E coli K1 is associated with invasive diseases in humans and in laboratory and domesticated animals. K1 isolates account for 80% of E. coli neonatal meningitis and comprise the majority of capsular types in neonatal septicaemia without meningitis and in childhood pyelonephritis. Passive administration of K1 antibodies prevented bacteraemia and meningitis in infant rats fed E. coli K1. Nonencapsulated derivatives of these invasive K1 strains did not cause bacteraemia in infant rats, although intestinal colonization was similar to that of the parent strains (M. Achtman and R.P.S., unpublished results). Several reports propose that the E. coli K1 capsular polysaccharide exerts an anti-phagocytic effect similar to that observed with other pathogenic encapsulated bacteria. One approach to studying whether the K1 antigen is sufficient to confer virulence of if other E. coli structures are necessary is to isolate the K1 genes for genetic and biochemical analysis. Recombinant DNA methodology provides a powerful tool for such an approach. Here, we report the molecular cloning of the E. coli K1 antigen genes. The cloned K1 genes synthesize a capsule in E. coli K12 indistinguishable chemically and immunologically from that of wild-type K1 strains.

This report describes the cloning, expression and characterization of two members of a novel human gene family of proteins, HBNF and MK, which exhibit neurite outgrowth-promoting activity. The HBNF cDNA gene codes for a 168-residue protein which is a precursor for a previously described brain-derived heparin-binding protein of 136 amino acids. The second human gene identified in this study, called MK, codes for a 143-residue protein (including a 22-amino acid signal sequence) which is 46% homologous with HBNF. Complementary DNA constructs coding for the mature HBNF and MK proteins were expressed in bacteria and purified by heparin affinity chromatography. These recombinant proteins exhibited neurite-outgrowth promoting activity, but lacked mitogenic activity. The HBNF gene is expressed in the brain of adult mice and rats, but only minimal expression of MK was observed in this tissue. Different patterns of developmental expression were observed in the embryonic mouse, with MK expression peaking in the brain between days E12 and E14 and diminishing to minimal levels in the adult, while expression of HBNF mRNA was observed to gradually increase during embryogenesis, reaching a maximal level at birth and maintaining this level into adulthood. Expression of these genes was also observed in the human embryonal carcinoma cell line, NT2/D1. Retinoic acid induced the expression of HBNF and MK 6- and 11-fold, respectively, in this cell line. Our studies indicate that HBNF and MK are members of a new family of highly conserved, developmentally regulated genes that may play a role in nervous tissue development and/or maintenance.

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