Essential protein with sulfite reductase activity required in assimilatory sulfate reduction pathway during both primary and secondary metabolism and thus involved in development and growth. DNA-binding protein that binds to both double-stranded and single-stranded DNA without significant sequence specificity to reversibly repress the transcriptional activity of chloroplast nucleoids by promoting DNA compaction and possibly regulate DNA replication. 3 H2O + hydrogen sulfide + 6 oxidized [2Fe-2S]-[ferredoxin] = 7 H(+) + 6 reduced [2Fe-2S]-[ferredoxin] + sulfite Binds 1 siroheme per subunit. Binds 1 [4Fe-4S] cluster per subunit. Inhibited by the tryptophan-modifying reagent, N-bromosuccinimide (NBS), by the lysine-modifying reagent, N-acetylsuccinimide and by the arginine-modifying reagent, phenylglyoxal. Complex formation with ferredoxin prevents these inhibitions. Optimum pH is 7.5. E is -285 +/- 5 mV for siroheme and -400 +/- 5 mV for 2Fe-2S at pH 7.5. Monomer (By similarity). Interacts with ferredoxin. Present in roots and leaves (at protein level). In leaves, sulfite reductase activity is detected in both bundle sheath and mesophyll cell types. Phosphorylated; this phosphorylation reduces DNA-binding. Belongs to the nitrite and sulfite reductase 4Fe-4S domain family.