an integral membrane protein that heterodimerizes with an alpha-3 chain, forming a receptor for many extracellular-matrix proteins including fibronectin, laminin, collagen, epiligrin and thrombospondin. . Beta 1 integrins recognize the amino-acid motif RGD in a wide array of ligands. Five alternatively spliced variants with alternate carboxy termini have been described. Two alternatively spliced isoforms have been described. Isoform beta-1a is widely expressed; other isoforms are generally expressed with a more restricted distribution. Isoform beta-1b is expressed in skin, liver, skeletal muscle, cardiac muscle, placenta, umbilical vein endothelial cells, neuroblastoma cells, lymphoma cells, hepatoma cells and astrocytoma cells. Isoforms beta-1c and beta-1c-2 are expressed in muscle, kidney, liver, placenta, cervical epithelium, umbilical vein endothelial cells, fibroblast cells, embryonal kidney cells, platelets and several blood cell lines. Isoform beta-c-2, rather than isoform beta-1c, is selectively expressed in primary t-cells. Isoform beta-1c is expressed in nonproliferating and differentiated prostate gland epithelial cells. Isoform beta-1d is expressed specifically in striated muscle (skeletal and cardiac muscle). Note: This description may include information from UniProtKB.