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Sidney Altman discovered that RNA moeity of RNAse P (M1 RNA) alone is able to perform enzymatic cleavage of ptRNA, which won him the Nobel Prize of Chemistry in 1989.

However, when I read the Nobel Lecture on Bioscience Report, Vol. 10, 1990, the figure on page 325 (the image below) confused me.

Altman, S. (1990) *Bioscience Reports* **10**:325.

I listed the relevant parts of the figure legend as follows:

(R: M1 RNA was added, P: [C5]=2x10^(-8) M, 20P: [C5]=4x10^(-7) M)

  • Lane 3: R+P, [Mg(II)]=10 mM. ptRNA cleaved.
  • Lane 5: R, [Mg(II)]=100 mM. ptRNA cleaved.
  • Lane 6: R+P, [Mg(II)]=100 mM. ptRNA NOT cleaved.
  • Lane 8: R+20P, [Mg(II)]=100 mM. ptRNA cleaved.

In Lane 3, RNAse P was formed and was able to catalyze cleavage; Lane 5 showed that M1 RNA with higher concentration of magnesium could function as enzyme.

But how did the addition of C5 protein, compared to Lane 5, inhibit the cleavage of ptRNA, as shown in Lane 6? (Or, how did raising [Mg(II)] to 100 mM compared to Lane 3 inhibit the reaction?)

And how come by increasing the concentration of C5 protein by a factor of 20 compared to Lane 6, M1 RNA was able to function again, as shown in Lane 8?

I would appreciate any kind of help, and sorry for my poor formatting.

Thanks.

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