Downstream effect - Sc nat5
From GO Public
http://www.yeastgenome.org/cgi-bin/locus.fpl?locus=NAT1 So this is annotated to N-terminal protein amino acid acetylation only, but is described as N-terminally acetylates many proteins, which influences multiple processes such as the cell cycle, heat-shock resistance, mating, sporulation, and telomeric silencing
This is part of the summary paragraph:
.....These enzymes are responsible for the N-terminal modification of more than half of yeast proteins (7). ....Deletion of NAT1 causes slow growth, failure to enter stationary phase, and defects in sporulation (1, 8). Cells lacking Nat1p or Ard1p show derepression of silent mating type loci; overexpression of Sir1p, a silent information regulator, can suppress this derepression phenotype (1, 9). NAT1 is also a modifier of position effect at telomeres; in nat1 mutants transcriptional repression is no longer seen near telomeres 10. Overexpression or deletion of NAT1 can lead to chromosomal instability (11). These mutant phenotypes suggest that the Nat1p/Ard1p complex may modify proteins important for chromatin structure and function.
In these instances, I don't know if the post translational modification annotation alone is enough? isn't the purpose of a post-translational modification to regulate a downstream process? we don't annotate histone deacetylases only to histone deacetylase, or kinases only to phosphorylation, we annotate the processes that they regulate to capture the biology.
I can see the issue here in that the effects are pleiotropic, but isn't this something we need to capture wht the GO annotation? Or is this a special case and it is more to do with the maturation of a protein and it isn't a regulatory event? The modification appears to be irreversible so maybe this means it isn't directy regulating the downstream events. This recent paper might be an arguement for NOT making the downstream annotations.
Science 327 (5968): 966-967 When the Beginning Marks the End Axel Mogk, and Bernd Bukau Acetylation of the amino terminus (Nt-acteylation) of a protein is one of the most common modifications, occurring in about 50% of yeast proteins and more than 80% of human proteins (1). It is catalyzed by N-terminal acetyltransferases, occurs predominantly on a nascent polypeptide chain as it is synthesized, and seems to be irreversible. So far, the biological role of Nt-acetylation has been enigmatic; only in a few cases has it been reported to affect protein functionality [for instance, nonacetylated actin is less efficient at assembling microfilaments (2)]. Controlling the activity of individual proteins cannot, however, explain the massive Nt-acetylation of bulk proteins. On page 973 in this issue, Hwang et al. (3) demonstrate that acetylation of the amino terminus of a protein can function as a degration signal (degron), revealing an entirely unexpected role of acetylation in protein turnover and possibly homeostasis.
The human ortholog has lots of annotations to downstream processes so this is a good example of potential annotation inconsistency http://www.uniprot.org/uniprot/Q9BXJ9