| Sumario: | The retinoblastoma protein (Rb) is a transcription regulator and key component of the
Rb/E2F/DP pathway which regulates progression of the cell cycle in plants and animals.
Within the pathway, Rb blocks E2F transcriptional activity consequently ensuring
restricted cell proliferation. Of great importance too, is a family of posttranslational
modifiers referred to as small ubiquitin-related modifiers (SUMO), whose modification
consequences include; sub cellular localization of proteins, alteration of protein to protein
interaction and regulation of transcriptional activity.
In order to study and depict the plant retinoblastoma related protein (RBR1) as a SUMO
substrate; its modification site was mutated to address the effect of the mutation on
protein localization. Additionally, an in-vitro assay was used to further illustrate the
consequences of the mutation. In protoplasts transfected with wild type RBR1 the protein
was solely present in the nucleus while those transfected with mutated RBR1, the protein
was seen in both the nucleus and the cytosol. From the in vitro SUMOylation assay it was
evident that while wild type RBR1 could be modified by SUMO, its mutated version
could not undergo modification.
The results from this study don’t only show RBR1 as a SUMO substrate; they also
suggest that modification by SUMO could be needed for its sub-cellular localization.
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