sentence: Northern analysis with a 3 ′ probe detected the full-length ( 1.7 kb ) eRF1 – 1 and a short ( about 0.5 kb ) RNA corresponding to a prominent 3 ′ fragment ( 3 ′ ) overaccumulating in xrn4 – 5 and xrn4 – 6 but barely visible in WT ( Figure 4A and B ) .