Def-6, a guanine nucleotide exchange factor for Rac1, interacts with the skeletal muscle integrin chain alpha7A and influences myoblast differentiation.

Integrin alpha7beta1 is the major laminin binding integrin receptor of muscle cells. The alpha7 chain occurs in several splice isoforms, of which alpha7A and alpha7B differ in their intracellular domains only. The fact that the expression of alpha7A and alpha7B is tightly regulated during skeletal muscle development suggests different and distinct roles for both isoforms.

The binding of Mss4 to alpha-integrin subunits regulates matrix metalloproteinase activation and fibronectin remodeling.

In four independent yeast two-hybrid screens with the integrin alpha-subunits alpha3A, alpha6A, alpha7A, and alpha7B, we identified the Mss4 protein, a nucleotide exchange factor for exocytic Rab GTPases, as a novel integrin interacting protein. We have previously shown that it binds to the conserved KXGFFKR region of integrin alpha-subunits located directly beneath the cell membrane. Here we show that the binding site for integrins on Mss4 is overlapping with those for Rab GTPases.

AtSUC8 and AtSUC9 encode functional sucrose transporters, but the closely related AtSUC6 and AtSUC7 genes encode aberrant proteins in different Arabidopsis ecotypes.

Three members of the Arabidopsis sucrose transporter gene family, AtSUC6-AtSUC8 (At5g43610; At1g66570; At2g14670), share a high degree of sequence homology in their coding regions and even in their introns and in their 5'- and 3'-flanking regions. A fourth sucrose transporter gene, AtSUC9 (At5g06170), which is on the same branch of the AtSUC-phylogenetic tree, shows only slightly less sequence homology. Here we present data demonstrating that two genes from this subgroup, AtSUC6 and AtSUC7, encode aberrant proteins and seem to represent sucrose transporter pseudogenes, whereas AtSUC8 and AtSUC9 encode functional sucrose transporters.