HIGH-MOBILITY GROUP PROTEIN-14 AND PROTEIN-17 CAN SPACE NUCLEOSOMES INVITRO

Recently we partially purified from Xenopus laevis ovaries a novel, AT P-dependent, spacing activity that can convert a DNA template consisti ng of irregularly spaced nucleosomes into a chromatin structure made u p of regularly spaced nucleosomes with a repeat length of 160-165 base pairs. In a second independent step, the longer spacing of higher euk aryotic chromatin can be generated by the addition of histone H1. The partially purified spacing fraction contains several proteins that dis play chromatographic properties and mobilities on polyacrylamide gels similar to high mobility group (HMG) proteins. For that reason, differ ent HMG proteins were tested for their ability to generate chromatin s tructures with regularly spaced nucleosomes. In this report, using two different nucleosome assembly systems, we show that the addition of p hosphorylated HMGs 14 and 17 to the histone octamer results in the for mation of chromatin with a repeat length of 160-165 base pairs. The re sults are similar to those obtained from studies of chromatin structur e in simple cells, such as fungi and yeast, and in active genes.