Abstract: Through function complementation of E. coli auxotrophs, the ultimate and pentultimate enzymes of the spinach riboflavin biosynthetic pathway have been cloned, namely, lumazine synthase (LS) and riboflavin synthase (RS). This invention relates to the isolation of nucleic acid fragments from plants or fungi that encode LS protein. The invention also relates to the isolation of nucleic acid fragments from plants or fungi that encode RS protein. In addition, the invention also relates to the construction of chimeric genes encoding all of a portion of LS, in sense or antisense orientation, wherein the expression of the chimeric gene results in production of altered levels of plant LS in a transformed host cell. Furthermore, the invention also relates to the construction of chimeric genes encoding all of a portion of RS, in sense or antisense orientation, wherein the expression of the chimeric gene results in production of altered levels of plant or fungal RS in a transformed host cell.