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Functional ribosomes synthesize proteins in all living cells and are composed of two labile associated subunits, which are made of rRNA and ribosomal proteins. The rRNA of the small 40S subunit (SSU) of the functional eukaryotic 80S ribosome decodes the mRNA molecule and the large 60S subunit (LSU) rRNA catalyzes protein synthesis. Recent fine structure determinations of the ribosome renewed interest in the role of ribosomal proteins in modulation of the core ribosomal functions. RpL10/Grc5p is a component of the LSU and is a multifunctional translational regulator, operating in 60S subunit biogenesis, 60S subunit export and 60S subunit joining with the 40S subunit. Here, we report that rpL10/Grc5p functionally interacts with the nuclear export factor Nmd3p in modulation of the cellular polysome complement and with the small subunit protein rpS6 in subunit joining and differential protein expression.

Biogenesis of an active ribosome complement and a dynamic cell surface complement are two major determinants of cellular growth. In yeast, the 60S ribosomal subunit protein RpL10p/Grc5p functions during successive stages in ribosome biogenesis, specifically rRNA processing, nucle(ol)ar preribosomal subunit assembly, nucleo-cytoplasmic transport and cytoplasmic maturation of ribosomes. Here, we report that a two-hybrid screen identified yeast genes SED1, ACS2 and PLB3 as encoding proteins physically interacting with both ribosomal RpL10p/Grc5p and its human homologue hRpL10p/QMp. SED1 encodes a differentially expressed cell wall protein which is proposed to be first transiently secreted to the plasma membrane as a GPI (glycosylated derivative of phosphoinositol)-anchored form and to be then transferred to the glucan layer of the cell wall. Ectopic expression of SED1 rescues both the aberrant growth phenotype and the translation defect of grc5-1(ts) temperature-sensitive cells. Furthermore, we report that Sed1p associates with translating ribosomes suggesting a novel, cytoplasmic role for Sed1p. ACS2 encodes one of the two yeast acetyl-CoA synthases and represents a key enzyme in one of several metabolic routes to produce acetyl-CoA, which in turn is indispensable for lipid biosynthesis. PLB3 encodes a phospholipase, which is active in the breakdown of membrane lipids. Our results support the view that Grc5p/RpL10p links ribosome function to membrane turnover and cell surface biogenesis.

among those patients. The development of cutaneous MFH in an immunocompromised host may be coincidental. However, it is also conceivable that long-term immunosuppression and, in addition, fair complexion and a stay in the tropics represent cofactors for tumour development. Although cutaneous MFHs in RTRs are very rare, the case reported here shows that cutaneous MFH with a poor prognosis may arise after RT, especially in patients with several risk factors. To our knowledge, this is the first reported case of cutaneous MFH of the scalp in an RTR. References1 Hartevelt MM, Bouwes Bavinck JN, Kootte AMM et al. Incidence of skin cancer after renal transplantation in the Netherlands. Transplantation 1990; 49:506-9. 2 Euvrard S, Kanitakis J, Claudy A. Skin cancers after organ transplantation. N Engl J Med 2003; 348:1681-91. 3 Penn I. Sarcomas in organ allograft recipients. Transplantation 1995; 60:1485-91. 4 Weiss SW, Goldblum JR. Malignant fibrohistiocytic tumors. In: Enzinger and Weiss's Soft Tissue Tumors (Weiss SW, Goldblum JR, eds), 4th edn. St Louis: Mosby CV 2001; 535-69. 5 Hafner J, Künzi W, Weinreich T. Malignant fibrous histiocytoma and atypical fibroxanthoma in renal transplant recipients. Dermatology 1999; 198:29-32. 6 Kanitakis J, Euvrard S, Montazeri A et al. Atypical fibroxanthoma in a renal graft recipient. J Am Acad Dermatol 1996; 35:262-4. 7 Camacho FM, Moreno JC, Murga M et al. Malignant fibrous histiocytoma of the scalp. Multidisciplinary treatment. J Eur Acad Dermatol Venereol 1999; 13:175-82. 8 Leite C, Goodwin JW, Sinkovics JG et al. Chemotherapy of malignant fibrous histiocytoma. A Southwest Oncology Group Report.