摘要：

Bacteriophage T4 codes for eight tRNAs, whose genes are tightly clustered between genes e and 57. The clustering of the transfer RNA genes suggested that these tRNAs are synthesized in a single transcriptional unit. Transcriptional experiments in vitro and experiments using the λ-T4 hybrid in vivo have supported this notion and located a T4 tRNA promoter. Detailed biochemical pathways of parts of the T4 tRNA processing are known. Maturation of the 3′ end precedes that of the 5′ end, and the 3′ ends of three dimeric precursors are matured in different ways by tRNA nucleotidyltransferase and ribonuclease BN. All T4 tRNAs require RNAase P for their 5′ maturation. Monomeric and dimeric precursors accumulate in the absence of RNAase P. How these monomeric and dimeric precursors are synthesized from their primary transcript, however, is poorly understood. Using the λ-T4 hybrid, carrying tRNA genes, and a fine restriction map of the tRNA gene cluster, we have determined the DNA sequence of the tRNA gene cluster, hoping that understanding of gene organization may suggest how the tRNAs are processed from their primary transcript. The DNA sequence of the tRNA gene cluster indicates that the monomeric and dimeric precursors are generated from their primary transcript by single endonucleolytic cleavages. We propose a model for the maturation of T4 tRNAs by predicting such an endonuclease (or endonucleases). The proposed endonucleolytic activities exist in the host. This model answers various questions about processing and reveals the unique features of T4 tRNA processing.

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