Cloning of an integrin beta subunit exhibiting high homology with integrin beta 3 subunit.

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Abstract
CDNAs for another .beta. subunit of the integrin family were isolated with the aid of polymerase chain reaction and sequenced. The combined cDNA sequence is 3110 base pairs (bp) in size and has one long open reading frame of 2388 bp. The deduced amino acid sequence is similar to those of other integrin .beta. subunits but does not correspond to .beta.1,.beta.2,.beta.3, or .beta.4 subunits. This .beta. subunit is divided by a membrane-spanning domain into a large extracellular domain at the N-terminal side and a small intracellular domain at the C-terminal side. The extracellular domain has a cysteine-rich region that contains four repeats of 68-cysteine motifs. All 56 cysteine residues found in the extracellular domains of other mature .beta. subunits are presented in this .beta. subunit. The .beta. subunit reported here has particularly high homology with the .beta.3 subunit. The mRNA for the molecule is .apprxeq. 3.5 kbp in size and is expressed in various cell types. Other researches have recently reported additional .beta. subunits that associate with the vitronectin receptor .alpha. subunit. The deduced amino acid sequence of this molecule contains the N-terminal partial amino acid sequence of one of these .beta. subunits, .beta.x. The .beta. subunit described herein seems to be identical to teh .beta.x subunit and to function as the .beta. subunit of a vitronectin receptor.