In 1959 Wacker and Vallee reported a ribonucleoprotein from liver; the material contained 0.1% chromium in addition to a few other metals [187, 188]. Chromium could not be removed by the addition of chelating agents. The purity of the material is unfortunately impossible to gauge from the report. RNA from a number of other sources was then examined; all RNA samples contained appreciable quantities of chromium, suggesting chromium accumulates in or is specifically associated with RNA [187, 188]. These observations are worthy of re-examination. Does Cr3+ just accumulate with RNA because of a propensity for chelating phosphate-type ligands or is there a specific role for chromium? This possible binding of chromium to nucleic acids could also potentially be related to possible toxic aspects of the metal (see Chapters 9-12).
Okada and coworkers have reported that Cr3+ stimulated RNA synthesis in vitro , but the relevance of this study is uncertain. These workers have also found that rats injected with CrCl3 and partially hepatectomized 24 hours later had increased hepatic nucleolar RNA synthesis accompanied by the production of a nucleolar Cr-containing protein of 70kDa [190, 191]. Whether this is biologically significant or an artifact requires additional study. This group has also reported that a chromatin-Cr complex showed enhanced template activity for in vitro RNA synthesis [192,193].
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