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CONTENTS Nucleotide sequence of k2The nucleotide sequence of k2 has been deter-mined7* and together with earlier data from the termini of the p l a~m i d~'~~* gives a total length of 13,457 bp encoding ten ORFs of 95 amino acids or more. These have been termed ORF1-ORFlO and their organization is shown in Figure 2. As with kl, the genome organization is very compact and these ORFs occupy over 97% of the plasmid. The aminoterminal coding regions of ORF8 and ORF9 diverge from an intergenic space of 1 bp, ORFl and ORF2 overlap for 4 bp on opposite strands and in two other instances (ORFs 2 and 3 , 4 and 5), ORFs on the same strand show partial overlap of 4-1 1 bp in different frames*. The sequence of a 7.7 kb XhoI-BamHI restriction fragment which encompasses the left-hand end of k2 has also been determineda5 and is in agreement with that of Tommasino et ~1 . '~ The complete sequence indicates TIRs of 182 bp whose sequence is not related to those of kl. On sequencing k2 DNA derived from both K . lactis and S . cerevisiae F 102-2, only one nucleotide difference *These conclusions differ slightly from those of Tommasino et who suggested that the divergent ORFs 8 and 9 overlap on different strands while ORFs 5 and 6 overlap on the same strand. However, because transcription data indicate that translation of ORFs 6 and 8 must commence at the second (ATG) see below), these two overlaps are removed.

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Sec1p/Munc18 (SM) proteins are essential for SNARE-mediated membrane trafficking. The formulation of unifying hypotheses for the function of the SM protein family has been hampered by the observation that two of its members bind their cognate syntaxins (Sxs) in strikingly different ways. The SM protein Vps45p binds its Sx Tlg2p in a manner analogous to that captured by the Sly1p–Sed5p crystal structure, whereby the NH2-terminal peptide of the Sx inserts into a hydrophobic pocket on the outer face of domain I of the SM protein. In this study, we report that although this mode of interaction is critical for the binding of Vps45p to Tlg2p, the SM protein also binds Tlg2p-containing SNARE complexes via a second mode that involves neither the NH2 terminus of Tlg2p nor the region of Vps45p that facilitates this interaction. Our findings point to the possibility that SM proteins interact with their cognate SNARE proteins through distinct mechanisms at different stages in the SNARE assembly/disassembly cycle.