Northern blot analysis of the aprIV transcript. Lanes: 1, control; 2 and 3, 0.5 and 1.0% GlcNAc, respectively; 4 and 5, 0.5 and 1.0% N-acetylchitobiose, respectively; 6, 0.5% glycol chitin; 7, 0.5% powdered chitin; 8, 1.0% skim milk. (A) Formaldehyde-agarose gel electrophoresis of the total RNA (1.2 μg) from the strain; (B) Northern blot analysis. The HindIII-SphI fragment (0.8 kb) from pAP45 was used as a probe.