Analysis of serine peptidases. Multiple sequence alignment (CLUSTALX) of protein sequences identified in a cDNA library of unfed/2 d fed or 6 d fed Dermacentor variabilis midguts (DvM) and tick serine peptidases found on genbank. Arrowheads conserved amino acids involved in the catalytic triad. Shading represents 100% identity (black) or similarity (grey) among the sequences. Alignments were conducted using CLUSTALX. D. variabilis (Dv), Ornithodoros moubata (Om), Haemaphysalis longicornis (Hl), Rhipicephalus appendiculatus (Ra).