Identification and characterization of novel isoforms of COP I subunits.
COP I-coated vesicles are involved in vesicular trafficking in the early secretory pathway. The COP I coat is composed of seven subunits, alpha-, beta-, beta'-, gamma-, delta-, epsilon-, and zeta-COPs. Evidence suggests, however, that there may be isoforms of the COP I subunits. In the present study, we identified homologs of gamma-COP (gamma2-COP; original gamma-COP is referred to as gamma1-COP in this paper) and of zeta-COP (zeta2-COP; original zeta-COP is referred to as zeta1-COP). gamma1- and gamma2-COPs, and zeta1- and zeta2-COPs share 80 and 75%, respectively, of amino acids. mRNAs for gamma2-COP and zeta2-COP are expressed ubiquitously, suggesting their fundamental role in cellular function. Immunofluorescence analysis shows that gamma2-COP and zeta2-COP are colocalized with beta-COP in the paranuclear cis-Golgi region. Yeast two-hybrid analysis indicates that gamma1- and gamma2-COPs can directly, albeit promiscuously, interact with zeta1- and zeta2-COPs. Like gamma1-COP, gamma2-COP can form a complex with beta-COP in vivo. The gamma1-COP-containing and gamma2-COP-containing complexes can similarly interact with the cytoplasmic domain of p23. These results indicate that gamma2-COP and zeta2-COP can form a COP I-like complex in place of gamma1-COP and zeta1-COP, respectively, and suggest that the COP I complex and the COP I-like complex are functionally redundant.
Futatsumori
M
M
Institute of Biological Sciences and Gene Experiment Center, University of Tsukuba, Tsukuba Science City, Ibaraki 305-8572, Japan.
Kasai
K
K
Takatsu
H
H
Shin
H W
HW
Nakayama
K
K
D000595:Amino Acid Sequence; D001693:Biological Transport, Active; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D020755:Coat Protein Complex I / Q000737:chemistry* / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D010957:Plasmids; D011487:Protein Conformation; D012333:RNA, Messenger / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D020755:Coat Protein Complex I; D012333:RNA, Messenger