Comparison of the deduced amino acid sequences of RpoT polymerases. Sequences from Nuphar (NaRpoTm1, NaRpoTm2 and NaRpoTp), Selaginella (SmRpoTm), Arabidopsis (AtRpoTm, AtRpoTp and AtRpoTmp) and Physcomitrella (PpRpoT1mp, PpRpoT2mp and PpRpoT3) were aligned using ClustalW. Accession numbers are as follows: AtRpoTm, P92969; AtRpoTmp, CAC17120; AtRpoTp, O24600; PpRpoTmp1, CAC95163; and PpRpoTmp2, CAC95164. PpRpoT3 is an RpoT amino acid sequence derived from the database of the Physcomitrella patens genome project http://www.phytozome.net/physcomitrella. In silico analysis of the genome as well as expressed sequence tag (EST) data strongly suggest that the sequence, designated as PpRpoT3, is a product of an RpoT gene with the conserved intron-exon structure of land plants that encodes a functional RNA polymerase (U. Richter, unpublished data). Black lines indicate conserved blocks in the RpoT polymerase family; functionally crucial residues [28, 29] are indicated by asterisks. The position of common introns is designated by filled triangles and PpRpoT2mp-specific introns by open triangles. Conserved amino acid positions (60%) are shaded.