HYPK promotes the activity of the Nα-acetyltransferase A complex to determine
Abstract
In humans, the Huntingtin yeast partner K (HYPK) binds to the ribosome-associated
N
⁇
-acetyltransferase A (NatA) complex that acetylates ~ 40% of the proteome in humans and
Arabidopsis thaliana
. However, the relevance of
Hs
HYPK for determining the human N-acetylome is unclear. Here, we identify the
At
HYPK protein as the first in vivo regulator of NatA activity in plants
. At
HYPK physically interacts with the ribosome-anchoring subunit of NatA and promotes N
⁇
-terminal acetylation of diverse NatA substrates. Loss-of-
At
HYPK mutants are remarkably resistant to drought stress and strongly resemble the phenotype of NatA-depleted plants. The ectopic expression of
Hs
HYPK rescues this phenotype. Combined transcriptomics, proteomics, and N-terminomics unravel that HYPK impairs plant metabolism and development, predominantly by regulating NatA activity. We demonstrate that HYPK is a critical regulator of global proteostasis by facilitating masking of the recently identified nonAc-X
2
/ N-degron. This N-degron targets many nonacetylated NatA substrates for degradation by the ubiquitin-proteasome system.
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