The first membrane spanning region of the lamin B receptor is sufficient for sorting to the inner nuclear membrane

Our findings here that the transmembrane region of LBR specifies localization to the inner nuclear membrane adds another example to the growing list of transmembrane segments that carry sequence-specific information rather than just serving as nonspecific tethering devices. The specific in-formation residing in the primary structure of the transmembrahe o~-helix appears to be decoded via specific interaction with another transmembrane c~-helix to form dimers. Such dimerization has been shown to be important in signal transduction (reviewed by Ullrich and Schlessinger, 1990; De Vos et al., 1992) and is likely to be involved in protein degradation (Bonifacino et al., 1990a,b) and in protein topogenesis (see above).