Abstract
Two cDNA clones termed H36-1 and H36-2 were isolated from a human liver cDNA library. Clone H36-1 appears to represent the recently isolated human serum proteins h37 and h42, which are two differently glycosylated forms of a protein antigenically related to human complement factor H. The H36-1 deduced protein sequence is 327 amino acid long and possesses a leader sequence. The secreted part of the protein is comprised of five tandem repeating units, termed short consensus repeats (SCRs). SCR 1 and 2 display high homology to the corresponding region of the recently isolated murine factor H-related cDNA clone 13G1. In contrast, the 3'-end of the H36-1 clone shows sequence homology to the 3'-end of human complement factor H. The second clone, H36-2, is nearly identical to H36-1. Within 1148 base pairs, where the two clones overlap, their nucleotide sequences differed at nine positions. One nucleotide exchange in the sequence of H36-2 which was located within SCR 1 creats a stop codon (TAA). Consequently, the corresponding mRNA cannot code for a functional protein, suggesting that this clone is a transcribed pseudogene. These two clones represent new human members of the family of proteins structurally related to complement factor H.
Highlights
Two cDNA clones termed H36-1 and H36-2 were motif is not limited to complement proteins, as additional isolated from a humalniver cDNA library
Nick Translation and Hybridization-For hybridization the followinginserts or fragments were used(i) a near full-length probe representing H36-2 cDNA; (ii) a 5'-fragment, the 290-bp DdeI fragment of H36-2. This fragment covered the 5'-untranslated region, the leader sequence, and the sequence encoding short consensus repeats (SCRs) 1; (iii)a 3'fragment, a cDNA clone representingposition 3233-3760 of the factor H cDNA. This sequence corresponds to SCR 18-20 of factor H and SCR 3-5 of H36-1;and (iv) in addition the 1050-hp cDNA clone representing the 3'-end of the human 1.8-kh factor H mRNA was used [9].The DNA fragments were labeled with,'"Pby random priming (Amersham Corp.) and used for hybridization a t 42 "C (5 X Denhardt's, 5 X SSC, 0.1% sodium dodecyl sulfate, 250 pg/ml denatured salmon sperm DNA, and 50% formamide)
Structural Analysis and Homology-Structural alignment the 5”untranslated region, the leader sequence and SCR 1of of the secreted protein encoded by the cDNA clone H36-1 boththe H36-1 and H36-2 sequences; and a 3’-fragment indicated that theprotein is comprised of five SCRs (Fig. 2A). representing SCR 18-20 of factor H, a region which is nearly
Summary
SCRs, which potentially evolved by geneduplication are con- related to therecently described human serum protein Served structural elements ina family of proteinstermed h42) [11].The H36-1 cDNA clone appears to represents the regulators of complement activation [4]. Members of this two differently glycosylated, factor H-related proteins. The costs of publication of this article were defrayed in part by the payment of page charges. This article must be hereby marked “aduertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. T h e nucleotide sequence(s) reportedin thispaperhas been submitted to theGenBankTM/EMBLDataBankwith accession umber(s) contains an internal stopcodon within SCR 1
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