Identification of a novel alternatively spliced isoform of the ribosomal uL10 protein

Alternative splicing is one of the key mechanisms extending the complexity of genetic information and at the same time adaptability of higher eukaryotes. As a result, the broad spectrum of isoforms produced by alternative splicing allows organisms to fine-tune their proteome; however, the functions of the majority of alternatively spliced protein isoforms are largely unknown. Ribosomal protein isoforms are one of the groups for which data are limited. Here we report characterization of an alternatively spliced isoform of the ribosomal uL10 protein, named uL108. The uL10 protein constitutes the core element of the ribosomal stalk structure within the GTPase associated center, which represents the landing platform for translational GTPases - trGTPases. The stalk plays an important role in the ribosome-dependent stimulation of GTP by trGTPases, which confer unidirectional trajectory for the ribosome, allosterically contributing to the speed and accuracy of translation. We have shown that the newly identified uL108 protein is stably expressed in mammalian cells and is primarily located within the nuclear compartment with a minor signal within the cytoplasm. Importantly, uL108 is able to bind to the ribosomal particle, but is mainly associated with 60S and 80S particles; additionally, the uL108 undergoes re -localization into the mitochondria upon endoplasmic reticulum stress induction. Our results suggest a specific stress-related dual role of uL108, supporting the idea of existence of specialized ribosomes with an altered GTPase associated center.