Transcription termination by RNA polymerase II is coupled to transcript 3' end 
formation. A large cleavage and polyadenylation complex containing the major 
poly(A) polymerase Pap1 produces mRNA 3' ends, whereas those of 
nonpolyadenylated snoRNAs in yeast are formed either by endonucleolytic cleavage 
or by termination, followed by trimming by the nuclear exosome. We show that 
synthesis of independently transcribed snoRNAs involves default polyadenylation 
of two classes of precursors derived from termination at a main 
Nrd1/Nab3-dependent site or a "fail-safe" mRNA-like signal. Poly(A) tails are 
added by Pap1 to both forms, whereas the alternative poly(A) polymerase Tfr4 
adenylates major precursors and processing intermediates to facilitate further 
polyadenylation by Pap1 and maturation by the exosome/Rrp6. A more important 
role of Trf4/TRAMP, however, is to enhance Nrd1 association with snoRNA genes. 
We propose a model in which polyadenylation of pre-snoRNAs is a key event 
linking their transcription termination, 3' end processing, and degradation.