A novel cDNA encoding ubiquitin-conjugating enzyme of homo sapiens

p53 interacts with a number of cellular proteins to form complexes which are probably crucial for its normal physiological function involving cell cycle control, gene regulation, cell differentiation, apoptosis and tumor suppression. To identify these proteins, we used the yeast two-hybrid system and screened a HeLa cDNA library. Six positive colonies were isolated from 1. 5 × 10⁶ transformants. The cDNA sequence of each positive colony was determined. Two novel cDNA fragments (p53BP1 and p53BP2) were cloned. These two cDNA fragments code for the same protein composed of 158 amino acids, which shows high similarity to the ubiquitin-conjugating enzyme (UBC9) of H. sapiens as well as to E2s from other organisms, such as UBC (76%) of C. elegans, HUS5 (66%) of S. pombe, UBC (66%) of A. thaliana and UBC9 (56%) of S. cerevisiae. A cDNA fragment from p53BP1 was used to probe a Northern blot containing poly(A)⁺ RNA from various human tissues and various cell lines. At high stringency this probe hybridized to a single mRNA of approximately 1. 2 kb that was expressed in heart, brain, placenta, liver, skeletal muscle, kidney, pancreas, spleen, thymus, prostate, testis, ovary, small intestine, colon, peripheral blood leukocyte, human cervical carcinoma cell (HeLa), human mammary carcinoma cell (MCF-7), human lymphoma cell (Jurkatt) and human teratocarcinoma cell (PA-I). It is not expressed in brain, lung, human lung carcinoma cell, human heptocellular carcinoma cell (HepG2) and human glioma cell (U251MG).