Ribonuclease protection analysis of Rh50 mRNAs. Total reticulocyte RNAs (12.5 μg) protected a 270 nt Rh50 fragment and a 207 nt XK fragment. Rh50 mRNA levels in AC, compared after normalizing them to the XK internal standard, were about 54% of those detected in the RhD-positive control. No Rh50 mRNA was detected in AL. RNA probes of 396 nt and 333 nt for Rh50 and XK, respectively, migrate very close to each other in the gel. A radiolabeled HaeIII digest of phage ◊X174 was used as a size marker.