NOA36 Protein Contains a Highly Conserved Nucleolar Localization Signal Capable of Directing Functional Proteins to the Nucleolus, in Mammalian Cells

de Melo, Ivan S.; Jimenez-Nuñez, Maria D.; Iglesias, Concepción; Campos-Caro, Antonio; Moreno-Sanchez, David; Ruiz, Felix A.; Bolívar, Jorge

We studied NOA36 subcellular localization using the Flag epitope as a reporter tag, with the aim of reproducing the nucleolar localization of the endogenous NOA36 ( Fig. 1 A) . For this, the Flag epitope fused to the amino terminal of NOA36 was localized at discrete points in the nucleus of transiently HeLa transfected cells, (Fig. 1 B and 1C) in 100% of the interphase cells, although in a 12.5% or the transfectants, a diffuse or punctuated cytoplasmic pattern could also be appreciated (Fig. 1D) . The nucleolar localization of Flag-NOA36 recombinant protein was confirmed by using an anti-UBF antibody as nucleolar marker [45] (Fig. 2C ). The nucleolar staining was not homogeneous, being localized mainly on the periphery of the nucleolus; this localization was more obvious in the larger nucleoli. From the data previously reported we concluded that NOA36 contains at least one nucleolar localization signal.