N-Acetylvalyl-tRNAYl (AcVal-tRNA 1) was bound to the P site of uniformly 32P-labeled 70S ribosomes from Escherichia coli and crosslinked to 16S RNA in the 30S ribosomal subunit by irradiation with light of300-400 nm. To identify the crosslinked nucleotide in 16S RNA, AcVal-tRNAY. l-16S [32P]RNA was digested completely with RNase TI and the band containing the covalently attached oligonucleotides from tRNA and rRNA was isolated by polyacrylamide gel electrophoresis. The crosslinked oligonucleotide, and the 32P-labeled rRNA moiety released from it by photoreversal of the crosslink at 254 nm, were then analyzed by secondary hydrolysis with pancreatic RNase A and RNase U2. The oligonucleotide derived from 16S RNA was found to be the evolutionarily conserved sequence, U-A-C-A-C-A-C-C-G1401, and the nucleotide crosslinked to tRNAI , C14W. The identity of the covalently attached residue in the tRNA was established by using AcVal-tRNAlv-16S RNA prepared from unlabeled ribosomes.This complex was digested to completion with RNase T1 and the resulting RNA fragments were labeled at the 3' end with [5'-32P]pCp. The crosslinked Ti oligonucleotide isolated from the mixture yielded one major end-labeled component upon photoreversal. Chemical sequence analysis demonstrated that this product was derived from the anticodon-containing pentadecanucleo-

The T-DNA regions of the root-inducing (Ri) plasmid pRiA4b of Agrobacterium rhizogenes were characterized. Two regions, designated TL-DNA and TR-DNA, were found to be integrated and stably maintained in the plant genome. The TL-DNA spanned a 15to 20-kilobase region of pRiA4b and was separated from the TR-DNA region by at least 15 kilobases of nonintegrated plasmid DNA. The TR-DNA region also spanned a 15to 20-kilobase region of pRiA4b and included a region of homology to the tms morphogenic loci of the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens. Eighteen deletions and 95 transposon insertions were generated in the T-DNA regions and tested for alterations in virulence. Insertions into four loci in the TL-DNA affected the morphology of root formation of Kalanchoe diagremontiana leaves and stems, but had no visible effects on other host plants. Insertions into two loci (tms-i and tms-2) in the TR-DNA eliminated virulence symptoms on all plants tested, with the exception of K. diagremontiana stems, where sparse root formation occurred. Complementation experiments with Ri and Ti plasmid T-DNA mutations indicate that the tms genes of the two plasmids serve similar functions and suggest a functional relationship between one or more genes of the TL-DNA and the cytokinin synthesis locus tmr of the Ti plasmid.

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