THE LOCATION OF UNTRANSCRIBED DNA-SEQUENCES WITHIN RAS GENES ESSENTIAL FOR ELICITING PLANT-GROWTH SUPPRESSION

Three heterologous ras DNA-coding sequences and their deletion derivat ives were introduced into plant cells to investigate the role of the r as-coding sequences, especially conserved regions, in eliciting growth inhibition. All three ras-coding sequences caused a similar inhibitio n of plant cell growth, and it was the conserved coding regions which were responsible for this inhibitory effect. The 493 bp conserved regi on within the v-Ha-ras-coding sequence was studied further, and was sh own to be responsible for the inhibitory effect. This region is conser ved (over 44%) among the three ras genes studied and encodes a catalyt ic region of the Ras protein. Small deletions at either the 5' or 3' e nd of this 493 bp sequence could abolish or dramatically reduce the in hibitory effect. A 36 bp region at the 5' end of the 493 bp region was found to be highly conserved between v-Ha-ras and eight different pla nt ras or ras-related genes based upon analysis of published sequences . Small deletions affecting this highly conserved 36 bp region complet ely abolished the inhibitory effect, while deletion of a similar numbe r of base pairs in adjacent regions did not. These results indicate th at plant growth inhibition by ras DNA requires small regions at both e nds of the 493 bp conserved region.