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The full-length sequence of tick salivary gland cDNA coding for a protein similar to metalloproteases (MP) of the reprolysin family is reported. The Ixodes scapularis MP is a 488 amino acid (aa) protein containing pre- and pro-enzyme domains, the zinc-binding motif HExxHxxGxxH common to metalloproteases, and a cysteine-rich region. In addition, the predicted amino-terminal sequences of I. scapularis MPs were found by Edman degradation of PVDF-transferred SDS/PAGE-separated tick saliva proteins, indicating that these putative enzymes are secreted. Furthermore, saliva has a metal-dependent proteolytic activity towards gelatin, fibrin(ogen), and fibronectin, but not collagen or laminin. Accordingly, I. scapularis saliva has a rather specific metalloprotease similar to the hemorrhagic proteases of snake venoms. This is the first description of such activity in tick saliva and its role in tick feeding and Borrelia transmission is discussed.