Clusters of Orthologous Genes Potentially Involved in the MBA Phase Variable System of Ureaplasmas. This table contains the NCBI locus tags for genes potentially involved in the MBA phase variable system. To form the NCBI locus tag add the serovar id and underscore before the gene number: UPA1_G0402; UUR12_A0163. Genes with tandem repeats are highlighted in green. A red box is drawn around the 4MBA genes expressed in ATCC type strains.