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Effect of Dietary Protein Restriction on Chromatin Proteins of Rat Mammary Gland^1,2,

National Dairy Research Institute, Karnal 132001, India

Rats were fed a diet containing either 20 or 5% casein from parturition onward. On the 14th day of lactation, ¹⁴C-leucine (U) and 6 hours prior to killing ³H-leucine (G) were administered intraperitoneally. On the 17th day of lactation, the rats were killed and mammary gland was excised. The wet weight of mammary tissue in 5% protein-fed groups was half that of the control. Nonhistone chromatin protein content of mammary gland chromatin was lower in the protein-restricted group. Chromatin was fractionated into transcriptionally active and inactive portions using bovine spleen DNase II. Though the proportion of either fraction of the total chromatin was not affected, the mass ratio of nonhistone chromatin protein to DNA of the active fraction was significantly less in 5% protein group than in 20% protein-fed animals. The histone:DNA ratio however appeared to be unchanged either between the two dietary groups or between the two fractions of chromatin. Qualitative differences in nonhistone chromatin proteins between the dietary groups became apparent after separation by SDS-polyacrylamide gel electrophoresis. Incorportion of the initial isotope as well as the average apparent turnover rate of nonhistone chromatin proteins of the protein-restricted group was less than the control. Turnover rate of histones was not affected by dietary protein level. Degradation constant of nonhistone proteins in different bands of polyacrylamide gels showed a dietary dependence.

KEY WORDS: • protein restriction • histones • nonhistone chromatin proteins • mammary gland

¹ National Dairy Research Institute—Karnal Publication Number 79–118.

² Partially supported by grants from the Department of Atomic Energy, Government of India.

³ Present address: College of Diary Science, Gujarat Agricultural University, Anand-388 110 India.

⁴ To whom reprint requests should be sent.

Manuscript received 8 June 1979.