What's the Relationship Between Synthesis and the Time of Day?
What's interesting here is this dip in synthesis. I really started doing DNA synthesis as a way to get an idea of growth rates in nature and then I got side tracked by this whole idea. What I started to think is, well gosh, if I were an organism, which I am, the last time I would want my DNA single stranded is right when the UV flux is high. And early afternoon seems to me to be a rather dangerous time to have my DNA single stranded. What if some of this had to do with the fact of UV flux in time? So, what I did, a good idea in these cases is to get a post doctorate; very clever. This is Charlie Cockell. He worked with me about a year ago. I said Charlie, what's known about DNA synthesis and the down regulation of DNA synthesis in response to UV? Eager beaver, potential post doc. He went to the library and found out that there in fact had been some lab studies done on E. coli, Escherichia coli, not to be confused with an Entamoebae coli, which is a protozoan. There were tissue culture cells studies showing that if you shined them with UV light you'd get a decrease DNA synthesis. We though ah-ha, that's all we need to test.
So what we did was we built Plexiglas boxes--these are 15 inches or so square--and we either put UV transparent Plexiglas on top, UV opaque Plexiglas or UV transparent with a mylar shield. And mylar blocks UV-B but not UV-A. Here's Charlie actually smiling and working in the field. When you work for me you not only have to work hard, you have to smile. How awful! This is why there are no pictures of me working out in the field. Anyway, if you don't believe me on these different screens, here's the spectrum. This is the names of the manufacturers that make UV opaque Plexiglas. The UV opaque screen cuts off at about 400 nanometers but lets the photosynthetically active radiation (400 to 700 nanometer) light through. Here's that mylar cut off and here's the UV transparent. That's way below most of the UV's on the earth.
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