Complementary DNA and derived amino acid sequence of the. cap alpha. subunit of human complement protein C8: evidence for the existence of a separate. cap alpha. subunit messenger RNA

Journal Article · Tue Jun 16 04:00:00 EDT 1987 · Biochemistry; (United States)

OSTI ID:6025113

Rao, A G; Howard, O M.Z.; Ng, S C; Whitehead, A S; Colten, H R; Sodetz, J M

The entire amino acid sequence of the ..cap alpha.. subunit (M/sub r/ 64,000) of the eight component of complement (C8) was determined by characterizing cDNA clones isolated from a human liver cDNA library. Two clones with overlapping inserts of net length 2.44 kilobases (kb) were isolated and found to contain the entire ..cap alpha.. coding region (1659 base pairs (bp)). The 5' end consists of an untranslated region and a leader sequence of 30 amino acids. This sequence contains an apparent initiation Met, signal peptide, and propeptide which ends with an arginine-rich sequence that is characteristic of proteolytic processing sites found in the pro form of protein precursors. The 3' untranslated region contains two polyadenylation signals and a poly(A)sequence. RNA blot analysis of total cellular RNA from the human hepatoma cell line HepG2 revealed a message size of approx.2.5 kb. Features of the 5' and 3' sequences and the message size suggest that a separate mRNA codes for ..cap alpha.. and argues against the occurrence of a single-chain precursor form of the disulfide-linked ..cap alpha..-lambda subunit found in mature C8. Analysis of the derived amino acid sequence revealed several membrane surface seeking domains and a possible transmembrane domain. Analysis of the carbohydrate composition indicates 1 or 2 asparagine-linked but no O-linked oligosaccharide chains, a result consistent with predictions from the amino acid sequence. Most significantly, it exhibits a striking overall homology to human C9, with values of 24% on the basis of identity and 46% when conserved substitutions are allowed. As described in an accompanying report this homology also extends to the ..beta.. subunit of C8.

• Research Organization: Univ. of South Carolina, Columbia
• OSTI ID: 6025113
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:12; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINO ACID SEQUENCE
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
COMPLEMENT
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
DNA
DNA SEQUENCING
GLANDS
ISOTOPES
LIGHT NUCLEI
LIVER
MAMMALS
MAN
MESSENGER-RNA
MOLECULAR STRUCTURE
NUCLEI
NUCLEIC ACIDS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
PRIMATES
PROTEINS
RADIOISOTOPES
RECOMBINANT DNA
RNA
STRUCTURAL CHEMICAL ANALYSIS
VERTEBRATES