H. walsbyi encodes halomucin, an extremely large protein homologous to mammalian mucins. GC content (C) and gene organization (B) of a 60.000 bp long region of the genome of H. walsbyi. This region contains the large, high GC gene encoding halomucin (hmu1) and the two capsular protein biosynthesis genes capC and capB. The domain organization of halomucin (A) reveals domains typically found in mammalian mucins. The letters D, S, V, G, and L indicate domains enriched for the corresponding amino acids. Halomucin expression is shown by detection of its mRNA via RT-PCR (D). cDNA was prepared by reverse transcription using primer sets numbered 1 to 7 the position of which correspond to the striped and numbered boxes in the hmu1 gene (B).