Northern blot of TM-transfected COS cells. Ten micrograms of total RNA from COS.TM-CR (A) and COSdel.238 (B) cells was separated on a denaturing formaldehyde-agarose gel as detailed in the Materials and Methods. mRNA for TM was detected with a specific radiolabeled cDNA probe. 28S and 18S ribosomal bands are shown on the right.