Northern blots of human and murine tissues for factor XI and contact activation protease expression. (A) Human tissue Northern blots hybridized with a full-length human factor XI cDNA probe, (B) murine tissue Northern blots hybridized with a full-length murine factor XI cDNA probe, and (C) human tissue Northern blots hybridized with either a full-length human factor XII or human prekallikrein cDNA probe. Blots were subsequently stripped and hybridized with a human β-actin cDNA probe to show equal lane loading of RNA. The position of molecular weight markers in kilobases is shown at the left of the figures.