Terminator element mutations affect both the efficiency and position of RNA polymerase I termination in Schizosaccharomyces pombe

RNA polymerase I transcripts, purified from Schizosaccharomyces pombe cells , terminate at three sites that precede 'Sal box'-like termination element (TE) sequences. Essential features in these elements were investigated by t he in vivo expression of targeted mutations. RNA analyses confirmed a funct ional significance for two of the elements (Boxes 1 and 3), but indicated t hat the third, less related, sequence (Box 2) does not function as a termin ation signal. The results further indicated that the most conserved residue s in the two active TEs, as well as adjacent regions, are also most critica l to function. Furthermore, some mutations in these elements or in immediat ely flanking sequences affect not only the efficiency of termination, but a lso alter the position of termination by as much as 35 nt. Since the elemen t is able to influence the site of termination over a surprisingly long str etch of DNA sequence, these observations suggest that the TE does not act s imply as a pause element by fixing the termination factor.