FIG. 6.

Conserved sequence blocks of the α-1,4-mannosyltransferase PIG-M. A. The first well-conserved block of PIG-M is one of the few hydrophilic regions and closely follows the first transmembrane domains (like in PIG-B). The sequence aligns very poorly with that of the α-1,2-mannosyltransferases. It is strongly conserved among the orthologs, with 15 invariant positions in 36 amino acids (20 when the Trypanosoma sequence, which deviates most from the consensus, is omitted). The D[I,V]D motif (boxed) was identified as essential for activity. (B and C) Two more blocks are strongly conserved, suggesting a tight requirement for a function that remains to be identified. The species and accession numbers are as follows: A. thaliana (At), CAC34506; H. sapiens (Hs), BAB18567; S. cerevisiae (Sc), CAB89880; T. brucei (Tb), BAB20994; and P. falciparum (Pf). For Saccharomyces the nucleotide entry Z49907 was used, as the corresponding protein entries such as CAB89880 are probably based on the wrong start codon. CS, consensus sequence. Symbols and figure preparation are as described in the legend to Fig. 3.