Northern blots of the mRNA (TRA1) probed with cloned fragment 15T01 and of the mRNA probed with the 15C01 in Mm subline cells. One microgram of poly(A)+RNA was isolated from Mm subline cells and Northern blotted as detailed in the Materials and Methods. The blots were first hybridized with 15T01 (clone 9; A) or 15C01 (clone 24; B; top), stripped, and then hybridized with β-actin (bottom). Size markers (in kilobases) are shown on the left.