HEP-COP, a novel human gene whose product is highly homologous to the alpha-subunit of the yeast coatomer protein complex.

A 4333-bp novel human cDNA sequence designated HEP-COP was isolated from the Hep3B hepatocellular carcinoma cell line by the RACE technique. Within HEP-COP was identified an ORF of 3672 bp encoding a deduced 1224-amino-acid (aa) sequence which exhibited striking homology with the 1201-aa sequence of RET1P, the alpha-subunit of the coatomer complex (alpha-COP) in Saccharomyces cerevisiae which participates in membrane transport between the endoplasmic reticulum and Golgi apparatus. The aa homology was highest in their N-terminal regions which each contained six WD-40 repeat motifs [Van der Voorn and Ploegh, FEBS Lett. 307 (1992) 131-134], and both proteins were predicted to be hydrophilic with similar estimated molecular masses of 138 324 and 135 599 Da, respectively. Northern blot hybridization demonstrated that HEP-COP was expressed in a wide range of human adult and fetal tissues. RT-PCR analysis revealed no differential expression of HEP-COP in 14 human cancer cell lines, as compared with normal control cells. Considering the close similarities between HEP-COP and yeast alpha-COP, and the ubiquitous expression of HEP-COP implying an essential cellular role, it is likely that HEP-COP is the human homologue of alpha-COP.