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Fig. 1. Expression patterns and multiple sequence alignment of Tetrahymena meiotic genes and proteins. (A) Expression of genes, demonstrated by RT-PCR. SPO11 is expressed only in meiosis. Of the two Tetrahymena HOP2 homologs, HOP2A is meiosis-specific and HOP2B is ubiquitously expressed. Likewise, two MND1-related genes show meiotic and ubiquitous expression, respectively. E, exponentially growing cells; S, cells growing under starvation conditions; numbers indicate the time after mixing of the cultures. RPL21 is a ubiquitously expressed control gene. (B) Multiple sequence alignment of the N-terminal–central-region of Hop2-group proteins that have highest sequence conservation within the family and show similarity to the `winged helix' fold. Protein-sequence identifiers are composed of two-letter species codes (Sc, Saccharomyces cerevisiae; Sp, Schizosaccharomyces pombe; Mm, Mus musculus; At, Arabidopsis thaliana; Tt, Tetrahymena thermophila) and common protein symbols. Accession numbers of the sequences used: NP_011482 (Sc), NP_001018191 (Sp), NP_032975 (Mm), NP_172791 (At), XP_001020981 (Tt Hop2A) and XP_001013509 (Tt Hop2B). Visualization was performed with Jalview with BLOSUM62-score/conservation shading (Clamp et al., 2004). Identical (*), strongly conserved (:) and weakly conserved (.) amino acids as well as predicted 
-helices (white bars) and β-strands (arrows) are indicated below the alignment. Tetrahymena TTHERM_01190440 protein (Hop2Bp) shows closer sequence similarity to members from other species than does TTHERM_00794620 protein (Hop2Ap). With a predicted length of 422 and 314 amino acids (aa), respectively, Hop2Bp and Hop2Ap would be notably longer than the other members of the Hop2 orthology group, which have around 220 aa.
