5-Methylcytidylic modification of in vitro transcript from the rat identifier sequence; evidence that the transcript forms a tRNA-like structure.

Previous studies showed that the rat identifier sequence, the rodent type 2 Alu family, the rabbit C family and the bovine or goat 73 bp repeat show remarkable resemblance with a few specific tRNA molecules (Sakamoto and Okada, J. Mol. Evol. in press). This paper reports 5-methylcytidylic modification of the in vitro transcript from the ID sequence, and provides further evidence that the transcript forms a tRNA-like structure in vitro. Fingerprint analysis and oligonucleotide mapping suggested that the sequence of the oligonucleotide containing 5-methylcytidine is CpCpm5CpUpGp, which corresponds to the extra and T psi stem regions in the secondary structure of phenylalanine tRNA. Since the sequence of the corresponding oligonucleotide in the phenylalanine tRNA is Cpm5CpCpUpGp, these results suggests that a tRNA (cytosine-5) methyl transferase recognizes the secondary structure of the transcript from the ID sequence rather than the primary sequence. The significance of this modification in relation to the functional role of the ID sequence is discussed.