The amino-terminal domain of the lamin B receptor is a nuclear envelope targeting signal

Rabbit antibodies against human hemoglobin that recognize chimpanzee a-globin were obtained from Dako Corporation (Carpinteria, CA). Rabbit antibodies against chicken hepatic lectin were a gift from Dr. K. Drickamer and have been previously described (Loeb and Drickamer, 1987) . Antibodies that recognize the amino-terminal domain of chicken LBR were made against a synthetic polypeptide of sequence S-P-K-Q-R-K-S-Q-S-S-S-S-S (The Rockefeller University/Howard Hughes Medical Institute Biopolymer Facility, New York, NY). The polypeptide was conjugated to keyhole limpet hemocyanin (Calbiochem-Novabiochem Corp., La Jolla, CA) by previously described methods (Muller et al., 1982) . The conjugate was injected into rabbits to produce polyelonal antibodies as described (Posnett et al., 1988) . Anti-LBR antibodies were purified from rabbit serum by affinity chromatography against the synthetic polypeptide coupled to Affi-Gel (Bio Rad Labs, Hercules, CA). Coupling using EDAC reagent was performed according to the manufacturer's instructions. Affinity chromatography was performed as described elsewhere (Harlow and Lane, 1988) . Anti-LBR antibodies were characterized by immunoblotting of proteins of chicken erythrocyte nuclear envelopes, rat liver nuclear envelopes and COS-7 cell lysates. Chicken erythrocyte nuclear envelopes were prepared as described for turkey erythrocytes (Worman et al., 1988) and rat liver nuclear envelopes were also prepared by methods used previously (Courvalin et al., 1990) . COS-'/cell lysates were made by scraping cells offpetri dishes and immediately boiling them in SDS-PAGE sample buffer (Laemmli, 1970) . SDS-PAGE was performed according to Laemmli (1970) . References for immunoblotting can be found elsewhere (Courvalin et al., 1990) .