The broad bean nodulin VfENOD18 is a member of a novel family of plant proteins with homologies to the bacterial MJ0577 superfamily.

Full-length transcript sequences were isolated from broad bean root nodules, which encode a novel nodulin designated VfENOD18. The corresponding transcripts were detected in early and in late stages of nodule development and were localized exclusively in the nitrogen-fixing zone III. The VfENOD18 sequence is not only homologous to a number of ESTs from various mono- and dicotyledonous plants, but also to the ATP-binding protein MJ0577 from Methanococcus jannaschii and to a range of bacterial proteins that belong to the MJ0577 superfamily. Hence, VfENOD18 is a member of a ubiquitous family of plant proteins that might function as ATP-binding proteins or ATPases. On the genomic level, VfENOD18 genes can be divided into two groups on the basis of differences in their 5' UTRs. One group lacks the 5' UTR region including the ATG initiation codon, whereas the second group contained the complete 5' UTR region. Further upstream of this VfENOD18 gene, a retrotransposon sequence was identified. The -14/-964 VfENOD18 promoter fragment was devoid of complete organ-specific elements known from other nodulin gene promoters. Nevertheless, this region was able to mediate full promoter activity in the central region of transgenic Vicia hirsuta root nodules.