Degradation of HIV-1 integrase by the N-end rule pathway

Human immunodeficiency virus type-1 (HIV-1) integrase catalyzes the irrever sible insertion of the viral genome into host chromosomal DNA. We have deve loped a mammalian expression system for the synthesis of authentic HIV-1 in tegrase in the absence of other viral proteins. Integrase, which bears a N- terminal phenylalanine, was found to be a short-lived protein in human embr yo kidney 293T cells. The degradation of integrase could be suppressed by p roteasome inhibitors. N-terminal phenylalanine is recognized as a degradati on signal by a ubiquitin-proteasome proteolytic system known as the N-end r ule pathway. The replacement of N-terminal phenylalanine with methionine, v aline, or glycine, which are stabilizing residues in the N-end rule, result ed in metabolically stabilized integrase proteins (half-life of N-terminal Met-integrase was at least 3 h). Conversely, the substitution of N-terminal phenylalanine with other destabilizing residues retained the metabolic ins tability of integrase. These findings indicate that the HIV-1 integrase is a physiological substrate of the N-end rule. We discuss a possible function al similarity to the better understood turnover of the bacteriophage Mu tra nsposase and functions of integrase instability to the maintenance and inte grity of the host cell genome.