Native receptor structure phosphorylation

Milgrom and co-workers [105] recently developed an immunogold method for detection of PR in the rabbit uterus and have examined the effect of hormone addition on receptor localization at the ultrastructural level. PR were found to be predominantly nuclear in the presence and absence of hormone, but a small amount was detectable in the cytoplasm which was not apparent at the light microscopical level. These cytoplasmic PR were localized over endoplasmic reticulum and clusters of free ribosomes and may likely represent newly synthesized protein. No PR were located in the plasma membrane. Within the nucleus, unoccupied PR were associated with condensed chromatin which became more dispersed after hormone addition. These ultrastructural studies indicate that steroid-free PR translocate from their site of synthesis in the cytoplasm to the nucleus in a hormone independent manner, and that addition of hormone changes their intranuclear localization. 

Whether unoccupied GR are totally nuclear is less clear. Immunocytochemical studies with anti-GR antibodies show both cytoplasmic and nuclear localization at the light level, and an increase in nuclear staining simultaneous with decreased cytoplasmic staining in response to addition of glucocorticoids [106-109]. It may well be that GR have a different intracellular distribution from the sex-steroid receptors. 

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As was previously established, the spatial structure of the receptor domains is altered by interaction with the hormone, with DNA, with other proteins, and by the state of the receptor phosphorylation. Different states of folding suppose that the receptor exhibits different surfaces that permit it to gain or to lose affinity for DNA sequences or for proteins, as they are components of the native receptor or of the transcriptional machinery. The different properties that... 

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