Effect of butyrate on the expression of TRA1 and NOR1 mRNAs in Mm-P cells. (A) Mm-P cells were cultured in the presence or absence of butyrate for 3 days, and then poly(A)+RNA was isolated. Northern blots were sequentially hybridized with the indicated probes. Size markers (in kilobases) are shown on the right. Relative amounts of TRA1 mRNA and NOR1 mRNA (B) were determined as described in the Materials and Methods.