Molecular cloning of two small GTP-binding proteins from human skeletal muscle

Two distinct cDNAs encoding small GTP-binding proteins were isolated from a human fetal skeletal muscle cDNA library. Nucleotide sequence analysis revealed that one clone encodes a protein of 218 amino acids, which shares highest amino acid identities (over 90%) with the members of YPT3 GTP-binding proteins subfamily and was termed H-YPT3; and the second clone encodes a protein of 201 amino acids, which exhibits strongest homology to rab1A, rab1B, and YPT1 at its N-terminus but diverges notably from these rab family members at the C-terminus. The second cDNA may represents a novel member of the small GTP-binding protein family and was designated H-ray. Northern blot analysis shows that both genes are ubiquitously expressed. Using a bacterial expression vector, each clone was overexpressed in Escherichia coli. The two bacterially produced proteins possess GTP-binding activity.