FIG. 1.

Models of L protein topology. (A) Model of the external topology of L with an exposed or translocated N-terminal pre-S domain; (B) model of the internal topology of L, present immediately after synthesis, with pre-S and TM1 being cytosolically disposed; (C) model of the intermediate topology, identified in mature particles, in which a small part of the C terminus of pre-S is exposed to the particle surface while the remainder is proposed to traverse the particle membrane and be located internally. The first transmembrane domain and the transmembrane anchor domain in S are indicated by boxes 1 and 2, respectively, but the third predicted but uncharacterized C-terminal transmembrane region is not shown. The N-terminal myristate is represented by the spiral. ext., exterior; int., interior.