A COMPARISON OF INTERNAL ELIMINATED SEQUENCES IN THE GENES THAT ENCODE 2 K-CHANNEL ISOFORMS IN PARAMECIUM-TETRAURELIA()

We examined both the somatic (macro-) and the germinal (micronuclear) DNAs that encode two K+-channel isoforms, PAK1 and PAK11, in Parameciu m tetraurelia. The coding regions of these two isoforms are 88% identi cal in nucleotides and 95% identical in amino acids. Their introns are also highly conserved. Even some of the internal eliminated sequences in PAK1 and PAK11 are clearly related. PAK1 has five IESs: PAK11 has four. The first (5'-most) IESs of the two genes are located at the sam e site in the coding sequence but differ in size. The 2nd IES in PAK1 (206-bp), the largest among the nine IESs, has no PAK11 counterpart. T he 3rd, 4th and 5th IESs in PAK1 have a counterpart in PAK11 that is s imilar in size and in sequence, and identical in its position in the c oding sequence. In addition, the first IES of PAK11 bears some resembl ance to the 4th one of PAK1. The similarities and differences between the two sets of IESs are discussed with respect to the origin and dive rgence of the two K+-channel isoforms.