Characterization of acidic ribosomal proteins from three developmental stages of the medfly Ceratitis capitata

Acidic proteins extracted with 0.5 M NH4Cl and 50% ethanol from ribosomes of the medfly Ceratitis capitata showed two major bands of MW 15 and 17 kD after SDS electrophoresis. Isoelectrofocusing of acidic proteins resolved two groups of bands at pH 4.5 and 3.5. Similar patterns were observed both from the acidic ribosomal protein fraction and from total ribosomes, treated with RNase. Treatment with alkaline phosphatase reduced the number of bands with a shift to a higher pI, indicating dephosphorylation. The phosphorylation pattern of the acidic proteins changed at three different stages of development, six day larvae, white pupae and 0-2 days old embryos. The two protein groups correspond to multi-phosphorylated forms of eucaryotic acidic ribosomal proteins P1 and P2. This was shown by immunoblotting with specific monoclonal antibodies.