A: Sequence comparison of exon 12a of Mtss1 in various mammals. Sequence rendered in grey letters are from adjoining exons. The * identifies conserved amino acids. Exon numbering is based on the murine sequences. B, C: Putative nuclear localization (B) and export (C) signals in Mtss1 are evolutionary conserved. B: Alignment of part of the IMD domain-sequences of Mtss1 and its structural relatives IRSp53 (also known as Baiap2) and Baiap2l1. The two nuclear localization signals identified are marked by a gray background. Basic amino acids are labeled red, and potential phosphorylation sites are marked green. The basic amino acids binding actin are marked by a yellow background. Note that these are conserved among Mtss1, IRSp53, and Baiap2l1, whereas the nuclear localization signal is found only in Mtss1, and a set of arthropod proteins which share the IMD domain of the Mtss1 type, but diverge from Mtss1 C-terminally. Note also that the nuclear localization signal centered about the basic, actin filament binding motif is immediately adjacent to the four amino acids encoded by exon 7 (shown in gray). C: The leucine-rich motif constituting a putative nuclear export signal inside the IMD is highly conserved for Mtss1. It is not found in the structural homologue, IRSp53. Also shown is the phylogenetic conservation of the nuclear export signal (NES) outside the IMD, which, in the mouse, is encoded by exon 14.