PALINDROMIC SEQUENCES PRECEDING THE TERMINATOR INCREASE POLYMERASE-III TEMPLATE ACTIVITY

Four consecutive T residues in the sense strand are sufficient to term inate transcription by RNA polymerase III (pol III). Previously we obs erved that compared with this minimally sufficient terminator, five T residues immediately preceded by a palindromic sequence increases tran scriptional expression both in vitro and in vivo, raising the question of whether a palindromic sequence has a role in pol III termination. Here we observe that site-directed mutations which eliminate the dyad symmetry of the palindromic sequence decrease transcriptional expressi on. Similar effects are observed whether dyad symmetry is eliminated i n regions of the palindrome which are proximal or distal with respect to the terminator. Compensatory mutations at either site to restore dy ad symmetry rescue transcriptional activity. These observations sugges t that a higher order structure, such as a RNA hairpin, immediately pr eceding the terminator increases pol III transcriptional activity.