Why is tumor tRNA hypomodified with respect to Q nucleoside

Nucleoside Q is found exclusively in the first position of the anticodon in tRNATyr, tRNAHis, tRNAAsn, and tRNAAsp (Kasai et al. 1975b, 1976). Its function is unknown, and long-term Q-deficient, germ-free mice appear normal (Reyniers et al. 1981). However, queuirie metabolism is altered in neoplasia. Many tumors exhibit Q-deficient tRNA (Katze 1975; Okada et al. 1978; Roe et al. 1979) and queuine addition to tumor-bearing mice can reverse tumor tRNA Q deficiency (Katze and Beck 1980; Nishimura et al., this volume pp. 401–412) and may inhibit tumor growth (Katze and Beck 1980). It is unlikely that Q-deficient tRNA is necessary for the neoplastic state since the careful study of Marini and Mushinski (1979; Mushinski and Marini, this volume pp. 121–132) shows widely varying, repeatable isoaccepting patterns (largely due to differences in Q content) for the Q family of tRNAs from several Balb/c mouse plasmacytomas with similar growth rates and size at harvest. These large differences among such a similar group of tumors suggest that the alteration in Q metabolism is secondary to the neoplastic process.