Ras is activated by transforming growth factor beta (TGF) in several cell types, but the biological consequences of this activation are largely unknown. We now show that ras mediates two stages in integrin 1-chain maturation: 1) glycosylation of the 86-kD core peptide, which is a TGF1-independent process, and 2) TGF1-mediated conversion of the 115-kD 1 integrin precursor into the mature 130-kD form. HD3 colon epithelial cells maintain elevated levels of integrin ␣21 heterodimers, strong binding to collagen I, and autocrine regulation by TGF1, which converts 1 integrin into the mature cell surface form. Each of three HD3 cell clones that stably express dominant negative ras (N17ras) exhibited abnormal glycosylation of the integrin 1-chain, decreased cell surface expression of the mature integrin 1, and impaired binding to collagen and laminin. Autocrine levels of TGF were not altered by expression of N17ras. The aberrant glycosylation of the integrin 1-chain was reversed by antisense oligonucleotides specific to the DNA sequence encoding the rasS17N mutation. Glycosylation of the 86-kD core peptide was delayed in the N17ras transfectants, but was not altered by either the addition of TGF1 or inhibition of autocrine TGF1. In contrast, conversion of the partially glycosylated 1 integrin precursor into the mature 130-kD isoform was accelerated by exogenous TGF1 and blocked by neutralizing antibody to autocrine TGF1 in control cell lines. Neither effect was seen in the N17ras transfectants, indicating that TGF1 modulates integrin 1-chain maturation by activating ras proteins. Cell fractionation studies demonstrated that this conversion takes place within the Golgi.