Northern blot analysis. Northern blot analysis was performed by a modification of a previously described procedure (Li and Pestka, 2008) . Briefly, probes (Table 1) were labeled with c-32 P by DNA 5# end-labeling system (Promega, Madison, WI) and purified by Micro-Bio-Spin6 chromatography column (Bio-Rad, Hercules, CA). Label incorporation was measured using a TopCount NXT (PerkinElmer, Shelton, CT). Total RNA (10 lg per lane) was separated on a 1.2% (wt/vol) formaldehyde denaturing agarose gel and transferred to a Biodyne membrane (Pall Gelman Laboratory, Ann Arbor, MI). After ultraviolet (UV) crosslinking (Stratagene, Cedar Creek, TX), membranes containing immobilized RNA were prehybridized for 1 h at 68°C and then incubated with [c-32 P]-labeled probes (1 3 10 6 cpm/ml) in Quickhyb solution (Stratagene) containing 200 lg/ml of herring sperm DNA at 68°C for 2 h. Blots were washed twice with 23 Side Scatter (SSC) containing 0.1% (wt/ vol) SDS at room temperature and once for 15 min with 0.13 SSC containing 0.1% (wt/vol) SDS at 50°C. The membranes were assembled with the Hyblot autoradiography film (Denville, Metuchen, NJ) into an X-ray exposure cassette and the film was developed after 24 h.