Cloning of a human multispanning membrane protein cDNA: evidence for a new protein family

We report the cloning of a human cDNA encoding a protein of calculated 68.8 kDa molecular mass, named hMP70. The deduced protein sequence shows a large N-terminal hydrophilic part and a C-terminal part with nine putative hydrophobic regions characteristic of integral transmembrane domains. Computer searches with sequence databases revealed homologies with three complete yeast proteins and with at least 19 human, 10 plant and one nematode short unidentified protein sequences translated from Expressed Sequence Tags (ESTs). Remarkably, this hMP70 protein retains between 27 and 31% overall sequence identity with the yeast proteins. We propose that hMP70 and related genes have evolved from a common ancestral gene and form a new multispanning membrane protein family which we call the MP70 protein family. Gene expression of hMP70 appears to be ubiquitous, as the mRNA is detectable in all human tissues analysed so far, as shown by Northern blot analysis. Furthermore, a protein of about 70 kDa is detectable in different mammalian cell lines, as shown by immunoblot analysis. From its widespread expression and conservation from yeast, plants to mammals, it is likely that hMP70 has a fundamental biological function in the cell.