Genetic And Biochemical-Characterization Of Bacillus-Subtilis-168 Mutants Specifically Blocked In The Synthesis Of The Teichoic-Acid Poly(3-O-Beta-D-Glucopyranosyl-N-Acetylgalactosamine 1-Phosphate) - Gnea, A New Locus, Is Associated With Udp-N-Acetylglucosamine 4-Epimerase Activity