Sialyltransferase gene family and external scales covering Bathycoccus. (a) Structural organization of the Bathycoccus RCC1105 sialyltransferase gene family. TM, transmembrane domain. L(1), S(2), (3) and VS(4) correspond to the four metazoan consensus motifs described for this gene family [43, 44]. Letters in the scheme below are the amino acid one-letter code with alternative possibilities for positions indicated between brackets. (b-d) Details of external scales covering Bathycoccus RCC1105 cells; white arrows indicate positions of external scales around the plasmic membrane while the black arrow indicates one intracellular scale inside a vesicle.