A workshop on the limitations of size of microbes in 1999 found that though modern nanobacteria can't be smaller in volume than the interior of a sphere of diameter 250 ± 50 nm, primitive microorganisms based on a single-polymer system could be. They cite the example of RNA based life, with ribozymes (catalytic RNA) taking the place of the much larger ribosomes as enzymes for cell replication. The cells also wouldn't have proteins and would have no need to translate DNA to mRNA. The result could be cells as small as a sphere 50 nm in diameter. These RNA World cells are one of the suggestions made to bridge the gap between abiotic chemistry and modern cells.