Since the double glycine mutation disrupted all of the GXXXG motifs, a corresponding decrease in either homo-or hetero-cisdimerization would be expected if these motifs were the sole mediators of this interaction. However, impaired dimerization could also occur if a reduction in GXXXG motifs destabilized cisdimers formed by single glycine mutants with a subsequent reduction in their steady state levels. Blue native-PAGE analysis showed that the apparent size of the double but not the single glycine mutants showed approximately a 100 kDA decrease in size, a shift consistent with impaired dimerization. Moreover, since single glycine to leucine mutations produced the growth suppressed phenotype but only double mutations hampered dimerization, it was concluded that even without an apparent effect on dimerization, glycine to leucine point mutations in the transmembrane domain had a profound effect on the growth phenotype produced by CEACAM1-4S.