The yeast homolog of human PinX1 is involved in rRNA and small nucleolar RNA maturation, not in telomere elongation inhibition

Abstract

In human cells, PinX1 protein has recently been shown to regulate telomere length by repressing the telomerase. In this work, we show that the putative yeast homolog of PinX1, encoded by the YGR280c open reading frame (ORF), is a new component of the ribosomal RNA processing machinery. The protein has a KK(E/D) C-terminal domain typical of nucleolar proteins and bears a putative RNA interacting domain widespread in eukaryotes called the G-patch. The protein was hence renamed Gnolp (G-patch nucleolar protein). GN01 deletion results in a large growth defect due to the inhibition of the pre-ribosomal RNA processing first cleavage steps at sites A0, A1, and A2. Furthermore, Gno1p is involved in the final 3′-end trimming of U18 and U24 small nucleolar RNAs. A mutational analysis showed that the G-patch of Gnolp is essential for both functions, whereas the KK(E/D) repeats are only required for U18 small nucleolar RNA maturation. We found that PinX1 complemented the gno1-Δ mutation, suggesting that it has a dual function in telomere length regulation and ribosomal RNA maturation in agreement with its telomeric and nucleolar localization in human cells. Conversely, we found that Gnolp does not exhibit the in vivo telomerase inhibitor activity of PinX1.