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Abstract
Laminin (Mr = 850,000) is a large basement membrane-specific glycoprotein composed of three chains: A, B1, and B2. Previously, we have reported the primary structure of the B1 chain of mouse laminin deduced from sequencing cDNA clones (Sasaki M., Kato, S., Kohno, K., Martin, G. R., and Yamada, Y. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 935-939). Here we report the isolation of overlapping cDNA clones spanning 7642 bases which encode the entire B2 chain. The nucleotide sequence of the clones contains an open reading frame of 4821 bases coding for a protein of 1607 amino acids including 33 amino acids of a presumptive signal peptide. The mRNA for the B2 chain contains 2.5 kilobases of 3'-untranslated region. The deduced amino acid sequence indicates that the B2 chain consists of six distinct domains, including two domains with alpha-helical, coiled-coil structures, two domains with cysteine-rich homologous repeats, and two globular domains. These structural features of the B2 chain are similar to those of the B1 chain. In addition, the amino acid sequences of the B2 and B1 chains demonstrate considerable homology, suggesting that the genes for these two chains arose from a common ancestor.
Highlights
Laminin (Mr= 850,000) is a large basement membrane-specific glycoprotein composed of three chains: A, B1, and B2
Globules are observed in the middle and at theend of each of the short arms, and a large globule is observed at the end of the long arm [6]
The B1 and B2 chains deduced from cDNA cloning [7] and from protein fragment analyses [8]suggested the occurrence of a coiled-coil structure in the long arm
Summary
Val. 262,No 35, Issue of December 15, pp. 1P7r1i1n1te-1d7i1n17U,1.S98.A7. From the Laboratory of Developmental Biology and Anomalies, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892. The deduced amino acid sequence indicates that the B2 chain consists of six distinct domains, including two domains with a-helical,coiled-coil structures, two domains with cysteine-richhomologousrepeats, and two globular domains. We reported the sequence of mouse laminin B1 chain, 1786amino acids, as deduced from nucleotide sequencing of its cDNA and predicted the presence of seven distinct structural domains [9]. We report the nucleotide sequence of cDNA coding for the entire B2 chain of mouse laminin. Starting with 10pgof poly(A)+ RNA, some 3 X lo6phage with recombinant DNA were obtained Another oligo(dT)-primed cDNA library was constructed from the differentiated F9 cell poly(A)+RNA by the modified Okayama-Berg method as described previously [9]. Two additional cDNA libraries were constructed using specific oligonucleotide primers from the differentiated F9 cell poly(A)+ RNA.
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