Variable amounts of translatable ferritin mRNA in bean leaves with various iron contents.

RNA was isolated from bean leaves with various iron and ferritin contents. The amount of translatable ferritin mRNA in these RNAs was determined by wheat-germ cell-free translation and immunoprecipitation with anti-bean seed ferritin serum. The levels of ferritin mRNA present in total RNA of the leaves are reflected by the in vivo levels of ferritin in the corresponding leaf tissues. This implies that the iron-dependent regulation of phytoferritin synthesis, in contrast with the regulation of animal ferritin synthesis, occurs at the level of transcription.

Two higher molecular weight forms related to ferritin are synthesizedin vitro by RNA from developing cotyledons and leaves ofPhaseolus vulgaris.

Using RNA from developing cotyledons and leaves of bean two products were synthesizedin vitro, with Mr 31000 and 31500 which are antigenically related to the subunit of phytoferritin (Mr 26500). The relative abundance of the two products is dependent on the type of tissue from which the RNA was derived. Evidence is presented for the assumption that both products are precursors of the phytoferritin subunit. The hypothesis is put forward that different transit sequences direct the phytoferritin subunits to different cell organelles.