Figure 1.

Amino acid sequence of Xenopus β subunits as deduced from the xo28 and xo32 cDNAs and comparison to sequences of mammalian β1b, β2a, β2b, β3, and β4 (A) and phylogenetic tree of calcium channel β subunits (B). (A) xoβ₃-28 is the reference. –, Same amino acid as in xoβ₃-28; –, gap; @, stop; rt, rat; rb, rabbit; hum, human; and xo, X. laevis oocyte. β2a differs from β2b only at the N terminus. β1, β1b splice variant. The phylogram shown in B was calculated by the neighbor-joining technique of Kimura, using version 8.0 of the gcg Sequence Analysis Software Package. Numbers in parenthesis next to names of β subunits are the GenBank accession numbers: for xo28, it is U33217U33217, and for xo32, it is U33218U33218.