Determination of rocker mutation.A, The sequence alteration in the rockermutant. Rocker contains a cytosine (C) to adenosine (A) change at nucleotide position 3929 that results in a threonine (T) to lysine (K) alteration at amino acid position 1310. B, Proposed transmembrane topography of the α 1A subunit and positions oftottering (tg), rolling (rol), leaner (la), and rocker (rkr) (indicated by arrows).