Mapping of protein positions in the ribosomal subunits was first achieved f
or the 30S subunit by means of neutron scattering about 15 years ago. Since
the 50S subunit is almost twice as large as the 30S subunit and consists o
f more proteins, it was difficult to apply classical contrast variation tec
hniques for the localisation of the proteins. Polarisation dependent neutro
n scattering (spin-contrast variation) helped to overcome this restriction.
Here a map of 14 proteins within the 50S subunit from Escherichia coli rib
osomes is presented including the proteins L17 and L20 that are not present
in archeal ribosomes. The results are compared with the recent crystallogr
aphic map of the 50S subunit from the archea Haloarcula marismortui. (C) 20
01 Elsevier Science BY. All rights reserved.